How do I get pylint to recognize MySQLdb members? - python-2.7

import MySQLdb
try:
dbcon = MySQLdb.connect(host=host_name, user=user_name,
passwd=password, db=db_name)
except MySQLdb.Error:
pass
getting this pylint warning
Module 'MySQLdb' has no 'Error' member (no-member)

The Best:
Using extension-pkg-whitelist option:
A comma-separated list of package or module names from where C extensions may be loaded. Extensions are loading into the active Python interpreter and may run arbitrary code
--extension-pkg-whitelist=_mysql
PyLint parses (by default) the source files, but in Python the shape of a module can change at runtime from the shape defined in the source file. This option tells PyLint to actually import the specified module, and use the runtime definition.
Note that since the MySQLdb package wraps a C extension, you have to pass the name of the C extension (_mysql) instead of the package name (MySQLdb). (source)
Not Bad:
Using unsafe-load-any-extension option
Allow loading of arbitrary C extensions. Extensions are imported into the active Python interpreter and may run arbitrary code.
--unsafe-load-any-extension=yes
You could use the unsafe-load-any-extension option, but that would load every available extension, with its' (potentially dangerous) initialization code. extension-pkg-whitelist is safer, because it only loads the specified modules.
The Worst:
Using disable option
# pylint: disable=no-member
It doesn't really solve the issue, but only makes PyLint silent.
Thanks to #PCManticore, the maintainer of PyLint. Here's the comment of the maintainer.
Thanks to #ZevSpitz, the contributor of the best answer and this not bad answer.

It may help to use the --extension-pkg-whitelist option:
--extension-pkg-whitelist=_mysql
pylint parses (by default) the source files, but in Python the shape of a module can change at runtime from the shape defined in the source file. This option tells pylint to actually import the specified module, and use the runtime definition.
Note that since the MySQLdb package wraps a C extension, you have to pass the name of the C extension (_mysql) instead of the package name (MySQLdb). (source)
You could use the unsafe-load-any-extension option, but that would load every available extension, with its' (potentially dangerous) initialization code. extension-pkg-whitelist is safer, because it only loads the specified modules.

Related

Python 2.7 Unable to import python file as a package [duplicate]

I've been here:
http://www.python.org/dev/peps/pep-0328/
http://docs.python.org/2/tutorial/modules.html#packages
Python packages: relative imports
python relative import example code does not work
Relative imports in python 2.5
Relative imports in Python
Python: Disabling relative import
and plenty of URLs that I did not copy, some on SO, some on other sites, back when I thought I'd have the solution quickly.
The forever-recurring question is this: how do I solve this "Attempted relative import in non-package" message?
ImportError: attempted relative import with no known parent package
I built an exact replica of the package on pep-0328:
package/
__init__.py
subpackage1/
__init__.py
moduleX.py
moduleY.py
subpackage2/
__init__.py
moduleZ.py
moduleA.py
The imports were done from the console.
I did make functions named spam and eggs in their appropriate modules. Naturally, it didn't work. The answer is apparently in the 4th URL I listed, but it's all alumni to me. There was this response on one of the URLs I visited:
Relative imports use a module's name attribute to determine that module's position in the package hierarchy. If the module's name does not contain any package information (e.g. it is set to 'main') then relative imports are resolved as if the module were a top level module, regardless of where the module is actually located on the file system.
The above response looks promising, but it's all hieroglyphs to me. So my question, how do I make Python not return to me "Attempted relative import in non-package"? has an answer that involves -m, supposedly.
Can somebody please tell me why Python gives that error message, what it means by "non-package", why and how do you define a 'package', and the precise answer put in terms easy enough for a kindergartener to understand.
Script vs. Module
Here's an explanation. The short version is that there is a big difference between directly running a Python file, and importing that file from somewhere else. Just knowing what directory a file is in does not determine what package Python thinks it is in. That depends, additionally, on how you load the file into Python (by running or by importing).
There are two ways to load a Python file: as the top-level script, or as a
module. A file is loaded as the top-level script if you execute it directly, for instance by typing python myfile.py on the command line. It is loaded as a module when an import statement is encountered inside some other file. There can only be one top-level script at a time; the top-level script is the Python file you ran to start things off.
Naming
When a file is loaded, it is given a name (which is stored in its __name__ attribute).
If it was loaded as the top-level script, its name is __main__.
If it was loaded as a module, its name is [ the filename, preceded by the names of any packages/subpackages of which it is a part, separated by dots ], for example, package.subpackage1.moduleX.
But be aware, if you load moduleX as a module from shell command line using something like python -m package.subpackage1.moduleX, the __name__ will still be __main__.
So for instance in your example:
package/
__init__.py
subpackage1/
__init__.py
moduleX.py
moduleA.py
if you imported moduleX (note: imported, not directly executed), its name would be package.subpackage1.moduleX. If you imported moduleA, its name would be package.moduleA. However, if you directly run moduleX from the command line, its name will instead be __main__, and if you directly run moduleA from the command line, its name will be __main__. When a module is run as the top-level script, it loses its normal name and its name is instead __main__.
Accessing a module NOT through its containing package
There is an additional wrinkle: the module's name depends on whether it was imported "directly" from the directory it is in or imported via a package. This only makes a difference if you run Python in a directory, and try to import a file in that same directory (or a subdirectory of it). For instance, if you start the Python interpreter in the directory package/subpackage1 and then do import moduleX, the name of moduleX will just be moduleX, and not package.subpackage1.moduleX. This is because Python adds the current directory to its search path when the interpreter is entered interactively; if it finds the to-be-imported module in the current directory, it will not know that that directory is part of a package, and the package information will not become part of the module's name.
A special case is if you run the interpreter interactively (e.g., just type python and start entering Python code on the fly). In this case, the name of that interactive session is __main__.
Now here is the crucial thing for your error message: if a module's name has no dots, it is not considered to be part of a package. It doesn't matter where the file actually is on disk. All that matters is what its name is, and its name depends on how you loaded it.
Now look at the quote you included in your question:
Relative imports use a module's name attribute to determine that module's position in the package hierarchy. If the module's name does not contain any package information (e.g. it is set to 'main') then relative imports are resolved as if the module were a top-level module, regardless of where the module is actually located on the file system.
Relative imports...
Relative imports use the module's name to determine where it is in a package. When you use a relative import like from .. import foo, the dots indicate to step up some number of levels in the package hierarchy. For instance, if your current module's name is package.subpackage1.moduleX, then ..moduleA would mean package.moduleA. For a from .. import to work, the module's name must have at least as many dots as there are in the import statement.
... are only relative in a package
However, if your module's name is __main__, it is not considered to be in a package. Its name has no dots, and therefore you cannot use from .. import statements inside it. If you try to do so, you will get the "relative-import in non-package" error.
Scripts can't import relative
What you probably did is you tried to run moduleX or the like from the command line. When you did this, its name was set to __main__, which means that relative imports within it will fail, because its name does not reveal that it is in a package. Note that this will also happen if you run Python from the same directory where a module is, and then try to import that module, because, as described above, Python will find the module in the current directory "too early" without realizing it is part of a package.
Also remember that when you run the interactive interpreter, the "name" of that interactive session is always __main__. Thus you cannot do relative imports directly from an interactive session. Relative imports are only for use within module files.
Two solutions:
If you really do want to run moduleX directly, but you still want it to be considered part of a package, you can do python -m package.subpackage1.moduleX. The -m tells Python to load it as a module, not as the top-level script.
Or perhaps you don't actually want to run moduleX, you just want to run some other script, say myfile.py, that uses functions inside moduleX. If that is the case, put myfile.py somewhere else – not inside the package directory – and run it. If inside myfile.py you do things like from package.moduleA import spam, it will work fine.
Notes
For either of these solutions, the package directory (package in your example) must be accessible from the Python module search path (sys.path). If it is not, you will not be able to use anything in the package reliably at all.
Since Python 2.6, the module's "name" for package-resolution purposes is determined not just by its __name__ attributes but also by the __package__ attribute. That's why I'm avoiding using the explicit symbol __name__ to refer to the module's "name". Since Python 2.6 a module's "name" is effectively __package__ + '.' + __name__, or just __name__ if __package__ is None.)
This is really a problem within python. The origin of confusion is that people mistakenly takes the relative import as path relative which is not.
For example when you write in faa.py:
from .. import foo
This has a meaning only if faa.py was identified and loaded by python, during execution, as a part of a package. In that case,the module's name
for faa.py would be for example some_packagename.faa. If the file was loaded just because it is in the current directory, when python is run, then its name would not refer to any package and eventually relative import would fail.
A simple solution to refer modules in the current directory, is to use this:
if __package__ is None or __package__ == '':
# uses current directory visibility
import foo
else:
# uses current package visibility
from . import foo
There are too much too long anwers in a foreign language. So I'll try to make it short.
If you write from . import module, opposite to what you think, module will not be imported from current directory, but from the top level of your package! If you run .py file as a script, it simply doesn't know where the top level is and thus refuses to work.
If you start it like this py -m package.module from the directory above package, then python knows where the top level is. That's very similar to java: java -cp bin_directory package.class
So after carping about this along with many others, I came across a note posted by Dorian B in this article that solved the specific problem I was having where I would develop modules and classes for use with a web service, but I also want to be able to test them as I'm coding, using the debugger facilities in PyCharm. To run tests in a self-contained class, I would include the following at the end of my class file:
if __name__ == '__main__':
# run test code here...
but if I wanted to import other classes or modules in the same folder, I would then have to change all my import statements from relative notation to local references (i.e. remove the dot (.)) But after reading Dorian's suggestion, I tried his 'one-liner' and it worked! I can now test in PyCharm and leave my test code in place when I use the class in another class under test, or when I use it in my web service!
# import any site-lib modules first, then...
import sys
parent_module = sys.modules['.'.join(__name__.split('.')[:-1]) or '__main__']
if __name__ == '__main__' or parent_module.__name__ == '__main__':
from codex import Codex # these are in same folder as module under test!
from dblogger import DbLogger
else:
from .codex import Codex
from .dblogger import DbLogger
The if statement checks to see if we're running this module as main or if it's being used in another module that's being tested as main. Perhaps this is obvious, but I offer this note here in case anyone else frustrated by the relative import issues above can make use of it.
Here's a general recipe, modified to fit as an example, that I am using right now for dealing with Python libraries written as packages, that contain interdependent files, where I want to be able to test parts of them piecemeal. Let's call this lib.foo and say that it needs access to lib.fileA for functions f1 and f2, and lib.fileB for class Class3.
I have included a few print calls to help illustrate how this works. In practice you would want to remove them (and maybe also the from __future__ import print_function line).
This particular example is too simple to show when we really need to insert an entry into sys.path. (See Lars' answer for a case where we do need it, when we have two or more levels of package directories, and then we use os.path.dirname(os.path.dirname(__file__))—but it doesn't really hurt here either.) It's also safe enough to do this without the if _i in sys.path test. However, if each imported file inserts the same path—for instance, if both fileA and fileB want to import utilities from the package—this clutters up sys.path with the same path many times, so it's nice to have the if _i not in sys.path in the boilerplate.
from __future__ import print_function # only when showing how this works
if __package__:
print('Package named {!r}; __name__ is {!r}'.format(__package__, __name__))
from .fileA import f1, f2
from .fileB import Class3
else:
print('Not a package; __name__ is {!r}'.format(__name__))
# these next steps should be used only with care and if needed
# (remove the sys.path manipulation for simple cases!)
import os, sys
_i = os.path.dirname(os.path.abspath(__file__))
if _i not in sys.path:
print('inserting {!r} into sys.path'.format(_i))
sys.path.insert(0, _i)
else:
print('{!r} is already in sys.path'.format(_i))
del _i # clean up global name space
from fileA import f1, f2
from fileB import Class3
... all the code as usual ...
if __name__ == '__main__':
import doctest, sys
ret = doctest.testmod()
sys.exit(0 if ret.failed == 0 else 1)
The idea here is this (and note that these all function the same across python2.7 and python 3.x):
If run as import lib or from lib import foo as a regular package import from ordinary code, __package is lib and __name__ is lib.foo. We take the first code path, importing from .fileA, etc.
If run as python lib/foo.py, __package__ will be None and __name__ will be __main__.
We take the second code path. The lib directory will already be in sys.path so there is no need to add it. We import from fileA, etc.
If run within the lib directory as python foo.py, the behavior is the same as for case 2.
If run within the lib directory as python -m foo, the behavior is similar to cases 2 and 3. However, the path to the lib directory is not in sys.path, so we add it before importing. The same applies if we run Python and then import foo.
(Since . is in sys.path, we don't really need to add the absolute version of the path here. This is where a deeper package nesting structure, where we want to do from ..otherlib.fileC import ..., makes a difference. If you're not doing this, you can omit all the sys.path manipulation entirely.)
Notes
There is still a quirk. If you run this whole thing from outside:
$ python2 lib.foo
or:
$ python3 lib.foo
the behavior depends on the contents of lib/__init__.py. If that exists and is empty, all is well:
Package named 'lib'; __name__ is '__main__'
But if lib/__init__.py itself imports routine so that it can export routine.name directly as lib.name, you get:
$ python2 lib.foo
Package named 'lib'; __name__ is 'lib.foo'
Package named 'lib'; __name__ is '__main__'
That is, the module gets imported twice, once via the package and then again as __main__ so that it runs your main code. Python 3.6 and later warn about this:
$ python3 lib.routine
Package named 'lib'; __name__ is 'lib.foo'
[...]/runpy.py:125: RuntimeWarning: 'lib.foo' found in sys.modules
after import of package 'lib', but prior to execution of 'lib.foo';
this may result in unpredictable behaviour
warn(RuntimeWarning(msg))
Package named 'lib'; __name__ is '__main__'
The warning is new, but the warned-about behavior is not. It is part of what some call the double import trap. (For additional details see issue 27487.) Nick Coghlan says:
This next trap exists in all current versions of Python, including 3.3, and can be summed up in the following general guideline: "Never add a package directory, or any directory inside a package, directly to the Python path".
Note that while we violate that rule here, we do it only when the file being loaded is not being loaded as part of a package, and our modification is specifically designed to allow us to access other files in that package. (And, as I noted, we probably shouldn't do this at all for single level packages.) If we wanted to be extra-clean, we might rewrite this as, e.g.:
import os, sys
_i = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
if _i not in sys.path:
sys.path.insert(0, _i)
else:
_i = None
from sub.fileA import f1, f2
from sub.fileB import Class3
if _i:
sys.path.remove(_i)
del _i
That is, we modify sys.path long enough to achieve our imports, then put it back the way it was (deleting one copy of _i if and only if we added one copy of _i).
Here is one solution that I would not recommend, but might be useful in some situations where modules were simply not generated:
import os
import sys
parent_dir_name = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
sys.path.append(parent_dir_name + "/your_dir")
import your_script
your_script.a_function()
#BrenBarn's answer says it all, but if you're like me it might take a while to understand. Here's my case and how #BrenBarn's answer applies to it, perhaps it will help you.
The case
package/
__init__.py
subpackage1/
__init__.py
moduleX.py
moduleA.py
Using our familiar example, and add to it that moduleX.py has a relative import to ..moduleA. Given that I tried writing a test script in the subpackage1 directory that imported moduleX, but then got the dreaded error described by the OP.
Solution
Move test script to the same level as package and import package.subpackage1.moduleX
Explanation
As explained, relative imports are made relative to the current name. When my test script imports moduleX from the same directory, then module name inside moduleX is moduleX. When it encounters a relative import the interpreter can't back up the package hierarchy because it's already at the top
When I import moduleX from above, then name inside moduleX is package.subpackage1.moduleX and the relative import can be found
Following up on what Lars has suggested I've wrapped this approach in an experimental, new import library: ultraimport
It gives the programmer more control over imports and it allows file system based imports. Therefore, you can do relative imports from scripts. Parent package not necessary. ultraimports will always work, no matter how you run your code or what is your current working directory because ultraimport makes imports unambiguous. You don't need to change sys.path and also you don't need a try/except block to sometimes do relative imports and sometimes absolute.
You would then write in somefile.py something like:
import ultraimport
foo = ultraimport('__dir__/foo.py')
__dir__ is the directory of somefile.py, the caller of ultraimport(). foo.py would live in the same directory as somefile.py.
One caveat when importing scripts like this is if they contain further relative imports. ultraimport has a builtin preprocessor to rewrite subsequent relative imports to ultraimports so they continue to work. Though, this is currently somewhat limited as original Python imports are ambiguous and there's only so much you can do about it.
I had a similar problem where I didn't want to change the Python module search
path and needed to load a module relatively from a script (in spite of "scripts can't import relative with all" as BrenBarn explained nicely above).
So I used the following hack. Unfortunately, it relies on the imp module that
became deprecated since version 3.4 to be dropped in favour of importlib.
(Is this possible with importlib, too? I don't know.) Still, the hack works for now.
Example for accessing members of moduleX in subpackage1 from a script residing in the subpackage2 folder:
#!/usr/bin/env python3
import inspect
import imp
import os
def get_script_dir(follow_symlinks=True):
"""
Return directory of code defining this very function.
Should work from a module as well as from a script.
"""
script_path = inspect.getabsfile(get_script_dir)
if follow_symlinks:
script_path = os.path.realpath(script_path)
return os.path.dirname(script_path)
# loading the module (hack, relying on deprecated imp-module)
PARENT_PATH = os.path.dirname(get_script_dir())
(x_file, x_path, x_desc) = imp.find_module('moduleX', [PARENT_PATH+'/'+'subpackage1'])
module_x = imp.load_module('subpackage1.moduleX', x_file, x_path, x_desc)
# importing a function and a value
function = module_x.my_function
VALUE = module_x.MY_CONST
A cleaner approach seems to be to modify the sys.path used for loading modules as mentioned by Federico.
#!/usr/bin/env python3
if __name__ == '__main__' and __package__ is None:
from os import sys, path
# __file__ should be defined in this case
PARENT_DIR = path.dirname(path.dirname(path.abspath(__file__)))
sys.path.append(PARENT_DIR)
from subpackage1.moduleX import *
__name__ changes depending on whether the code in question is run in the global namespace or as part of an imported module.
If the code is not running in the global space, __name__ will be the name of the module. If it is running in global namespace -- for example, if you type it into a console, or run the module as a script using python.exe yourscriptnamehere.py then __name__ becomes "__main__".
You'll see a lot of python code with if __name__ == '__main__' is used to test whether the code is being run from the global namespace – that allows you to have a module that doubles as a script.
Did you try to do these imports from the console?
Relative imports use a module's name attribute to determine that module's position in the package hierarchy. If the module's name does not contain any package information (e.g. it is set to 'main') then relative imports are resolved as if the module were a top level module, regardless of where the module is actually located on the file system.
Wrote a little python package to PyPi that might help viewers of this question. The package acts as workaround if one wishes to be able to run python files containing imports containing upper level packages from within a package / project without being directly in the importing file's directory. https://pypi.org/project/import-anywhere/
In most cases when I see the ValueError: attempted relative import beyond top-level package and pull my hair out, the solution is as follows:
You need to step one level higher in the file hierarchy!
#dir/package/module1/foo.py
#dir/package/module2/bar.py
from ..module1 import foo
Importing bar.py when interpreter is started in dir/package/ will result in error despite the import process never going beyond your current directory.
Importing bar.py when interpreter is started in dir/ will succeed.
Similarly for unit tests:
python3 -m unittest discover --start-directory=. successfully works from dir/, but not from dir/package/.

Why does this script not work if the file has a .py extension?

I'm following the instructions in the Coinbase API guide Coinbase Guide The first line of the code is to simply load the Coinbase library:
from coinbase.wallet.client import Client
I'm using IDLE as the IDE. If I work on a file with no extension (e.g. simply called 'coinbase') then the examples in the guide work fine.
If I work on a file with the standard Python extension (e.g. 'coinbase.py') it does not load the Coinbase library and errors out! The error message is:
ImportError: No module named wallet.client
I think this may not necessarily Coinbase related, and perhaps I'm doing something fundamentally wrong. Answers appreciated.
Remember that all python files are seen by python as modules.
So when you write a script called coinbase.py, python will see it as a module and let you import it with import coinbase. Doing so you are shadowing the real coinbase module that you meant to import, hence the error.
To fix the problem simply avoid calling your files with existing module names (unless of course you intend to shadow them).

Tkinter module compilation error - 2.5.2 needed

I have a decently long program that I have been trying to compile. I have tried py2exe and cx_Freeze, both seem to come up with this problem.
I used the following setup.py file to compile my program:
import sys
from cx_Freeze import setup, Executable
base = None
if sys.platform == 'win32':
base = 'Win32GUI'
executables = [
Executable('version_3_2.py', base=base)
]
setup(name='version_3_2',
version='0.32',
description='desc',
executables=executables
)
From running this using
python setup.py build
The executable is created.
From running the executable, i was given a traceback stating that
TclError: Can't find a usable init.tcl in the following directories:
C:/Python27/build/lib/tcl8.5
and a bunch of other directories
From adding all of the tkinter and tcl files and folers into a couple of those directories i get the next traceback from executing:
C:/Python27/build/lib/tcl8.5/init.tcl: version conflict for package "Tcl":
have 8.5.15, need exactly 8.5.2
version conflict for package "Tcl": have 8.5.15, need exactly 8.5.2
while executing
"package require -exact Tcl 8.5.2"
(file "C:/Python27/build/lib/tcl8.5/init.tcl" line 20)
invoked from within
"source C:/Python27/build/lib/tcl8.5/init.tcl"
("uplevel" body line 1)
invoked from within
"uplevel #0 [list source $tclfile]"
I'm not entirely sure what to do. Several solutions like How to correct TCL_LIBRARY and TK_LIBRARY with py2exe and Py2exe with Tkinter have not worked.
Any Ideas?
You need to match exactly the libtcl8.5.dll (or whatever the name is on your system) and the init.tcl (and related files) because they are both part of the same Tcl installation. If you change one out, you must change the other as well. How exactly you've mangled your installation I'm not quite sure, but mangled it surely is. Also be aware that in Tcl 8.5 (and before), it's strongly advised to match the Tk version precisely to it as well; we relax this requirement in 8.6 but you're not using that…
(Note that this is different from the way that normal dependencies work in Tcl; typically a program will depend on a minimum API version, not an exact one.)
Since you've got a binary build of 8.5.15 in use, you might as well use the script files for that version too. I suggest getting the Tcl source distribution for 8.5.15 from SourceForge and grabbing the files out of the library directory in there. You probably only need the .tcl files directly in there (especially init.tcl of course!) and not in any of the subdirectories, as the subdirectories are for official add on packages and those aren't so tightly bound to Tcl versions.

Building Python extension module with distutils

I'm using distutils to build a Python extension module written in C++. The problem I have is that in order to compile the extension module, I need to link with a certain shared library. This requires setting an additional compiler flag. So, I searched through the Python docs and found out about the extra_compile_args property of the Extension object. So I tried the following:
from distutils.core import setup, Extension
module = Extension('test', sources = ['test.cpp'])
module.extra_compile_args = ['--std=c++0x', '-l mylib'];
setup(name = 'test', version = '1.0', ext_modules = [module])
This seems to compile, except when I import my module in Python it throws an ImportError exception due to an undefined symbol. So, apparently the library didn't link properly. So I tried writing a throw away C++ program which linked with the shared library, and it ran fine. Then I realized something really odd is going on with distutils, because if I add a compile argument that links to a bogus library name, distutils just compiles everything with no problem:
module.extra_compile_args = ['--std=c++0x', '-l some_fake_library'];
When I run setup.py build, the build runs with no errors!
So, what's going on here? How can I compile an extension module that requires linkage to a shared library?
There's actually a special option for that.
For example:
libraries=["rt"]
You leave off the option and lib parts.
One of the purposes of distutils is to make your code not dependent on a single compiler. Your "-l somelib" looks like it's meant to work with GCC (even though it should be "-lsomelib", no space). This is why you use the libraries option to the Extension class. Distutils will then pass the appropriate link command to whatever compiler it's using.
You can also look at the actual build commands distutils is using and execute them yourself to see what is going wrong.

Py_Initialize fails - unable to load the file system codec

I am attempting to put together a simple c++ test project that uses an embedded python 3.2 interpreter. The project builds fine but Py_Initialize raises a fatal error:
Fatal Python error: Py_Initialize: unable to load the file system codec
LookupError: no codec search functions registered: can't find encoding
Minimal code:
#include <Python.h>
int main (int, char**)
{
Py_Initialize ();
Py_Finalize ();
return 0;
}
The OS is 32bit Vista.
The python version used is a python 3.2 debug build, built from sources using VC++ 10.
The python_d.exe file from the same build runs without any problems.
Could someone explain the problem and how to fix it? My own google-fu fails me.
EDIT 1
After going through the python source code I've found that, as the error says, no codec search functions have been registered. Both codec_register and PyCodec_Register are as they should be. It's just that nowhere in the code are any of these functions called.
I don't really know what this means as I still have no idea when and from where these functions should have been called. The code that raises the error is entirely missing from the source of my other python build (3.1.3).
EDIT 2
Answered my own question below.
Check the PYTHONPATH and PYTHONHOME environment variables and make sure they don't point to Python 2.x.
http://bugs.python.org/issue11288
Parts of this have been mentioned before, but in a nutshell this is what worked for my environment where I have multiple Python installs and my global OS environment set-up to point to a different install than the one I attempt to work with when encountering the problem.
Make sure your (local or global) environment is fully set-up to point to the install you aim to work with, e.g. you have two (or more) installs of, let's say a python27 and python33 (sorry these are windows paths but the following should be valid for equivalent UNIX-style paths just as well, please let me know about anything I'm missing here (probably the DLLs path might differ)):
C:\python27_x86
C:\python33_x64
Now, if you intend to work with your python33 install but your global environment is pointing to python27, make sure you update your environment as such (while PATH and PYTHONHOME may be optional (e.g. if you temporarily work in a local shell)):
PATH="C:\python33_x64;%PATH%"
PYTHONPATH="C:\python33_x64\DLLs;C:\python33_x64\Lib;C:\python33_x64\Lib\site-packages"
PYTHONHOME=C:\python33_x64
Note, that you might need/want to append any other library paths to your PYTHONPATH if required by your development environment, but having your DLLs, Lib and site-packages properly set-up is of prime importance.
Hope this helps.
The core reason is quite simple: Python does not find its modules directory, so it can of course not load encodings, too
Python doc on embedding says "Py_Initialize() calculates the module search path based upon its best guess" ... "In particular, it looks for a directory named lib/pythonX.Y"
Yet, if the modules are installed in (just) lib - relative to the python binary - above guess is wrong.
Although docs says that PYTHONHOME and PYTHONPATH are regarded, we observed that this was not the case; their actual presence or content was completely irrelevant.
The only thing that had an effect was a call to Py_SetPath() with e.g. [path-to]\lib as argument before Py_Initialize().
Sure this is only an option for an embedding scenario where one has direct access and control over the code; with a ready-made solution, special steps may be necessary to solve the issue.
Ran into the same thing trying to install brew's python3 under Mac OS! The issue here is that in Mac OS, homebrew puts the "real" python a whole layer deeper than you think. You would think from the homebrew output that
$ echo $PYTHONHOME
/usr/local/Cellar/python3/3.6.2/
$ echo $PYTHONPATH
/usr/local/Cellar/python3/3.6.2/bin
would be correct, but invoking $PYTHONPATH/python3 immediately crashes with the abort 6 "can't find encodings." This is because although that $PYTHONHOME looks like a complete installation, having a bin, lib etc, it is NOT the actual Python, which is in a Mac OS "Framework". Do this:
PYTHONHOME=/usr/local/Cellar/python3/3.x.y/Frameworks/Python.framework/Versions/3.x
PYTHONPATH=$PYTHONHOME/bin
(substituting version numbers as appropriate) and it will work fine.
From python3k, the startup need the encodings module, which can be found in PYTHONHOME\Lib directory.
In fact, the API Py_Initialize () do the init and import the encodings module.
Make sure PYTHONHOME\Lib is in sys.path and check the encodings module is there.
I had this issue with python 3.5, anaconda 3, windows 7 32 bit. I solved it by moving my pythonX.lib and pythonX.dll files into my working directory and calling
Py_SetPythonHome(L"C:\\Path\\To\\My\\Python\\Installation");
before initialize so that it could find the headers that it needed, where my path was to "...\Anaconda3\". The extra step of calling Py_SetPythonHome was required for me or else I'd end up getting other strange errors where python import files.
I just ran into the exact same problem (same Python version, OS, code, etc).
You just have to copy Python's Lib/ directory in your program's working directory ( on VC it's the directory where the .vcproj is )
There appears to be something going wrong with the release build either failing to include the appropriate codecs or else misidentifying the codec to use for system APIs. Since the python_d executable is working, what does that return for os.getfsencoding()? (Use the C API to call that between your Initialize/Finalize calls)
I had the same issue and found this question. However from the answers here I was not able to solve my problem. I started debugging the cpython code and thought that I might be discovered a bug. Therefore I opened a issue on the python issue tracker.
My mistake was that I did not understand that Py_SetPath clears all inferred paths.
So one needs to set all paths when calling this function.
Link to the issue conversation
For completion I also copied the most important part of the conversation below.
My original issue text
I compiled the source of CPython 3.7.3 myself on Windows with Visual Studio 2017 together with some packages like e.g numpy. When I start the Python Interpreter I am able to import and use numpy. However when I am running the same script via the C-API I get an ModuleNotFoundError.
So the first thing I did, was to check if numpy is in my site-packages directory and indeed there is a folder named numpy-1.16.2-py3.7-win-amd64.egg. (Makes sense because the python interpreter can find numpy)
The next thing I did was to get some information about the sys.path variable created when running the script via the C-API.
#### sys.path content ####
C:\Work\build\product\python37.zip
C:\Work\build\product\DLLs
C:\Work\build\product\lib
C:\PROGRAM FILES (X86)\MICROSOFT VISUAL STUDIO\2017\PROFESSIONAL\COMMON7\IDE\EXTENSIONS\TESTPLATFORM
C:\Users\rvq\AppData\Roaming\Python\Python37\site-packages
Examining the content of sys.path I noticed two things.
C:\Work\build\product\python37.zip has the correct path 'C:\Work\build\product\'. There was just no zip file. All my files and directory were unpacked. So I zipped the files to an archive named python37.zip and this resolved the import error.
C:\Users\rvq\AppData\Roaming\Python\Python37\site-packages is wrong it should be C:\Work\build\product\Lib\site-packages but I dont know how this wrong path is created.
The next thing I tried was to use Py_SetPath(L"C:/Work/build/product/Lib/site-packages") before calling Py_Initialize(). This led to
Fatal Python Error 'unable to load the file system encoding'
ModuleNotFoundError: No module named 'encodings'
I created a minimal c++ project with exact these two calls and started to debug Cpython.
int main()
{
Py_SetPath(L"C:/Work/build/product/Lib/site-packages");
Py_Initialize();
}
I tracked the call of Py_Initialize() down to the call of
static int
zipimport_zipimporter___init___impl(ZipImporter *self, PyObject *path)
inside of zipimport.c
The comment above this function states the following:
Create a new zipimporter instance. 'archivepath' must be a path-like
object to a zipfile, or to a specific path inside a zipfile. For
example, it can be '/tmp/myimport.zip', or
'/tmp/myimport.zip/mydirectory', if mydirectory is a valid directory
inside the archive. 'ZipImportError' is raised if 'archivepath'
doesn't point to a valid Zip archive. The 'archive' attribute of the
zipimporter object contains the name of the zipfile targeted.
So for me it seems that the C-API expects the path set with Py_SetPath to be a path to a zipfile. Is this expected behaviour or is it a bug?
If it is not a bug is there a way to changes this so that it can also detect directories?
PS: The ModuleNotFoundError did not occur for me when using Python 3.5.2+, which was the version I used in my project before. I also checked if I had set any PYTHONHOME or PYTHONPATH environment variables but I did not see one of them on my system.
Answer
This is probably a documentation failure more than anything else. We're in the middle of redesigning initialization though, so it's good timing to contribute this feedback.
The short answer is that you need to make sure Python can find the Lib/encodings directory, typically by putting the standard library in sys.path. Py_SetPath clears all inferred paths, so you need to specify all the places Python should look. (The rules for where Python looks automatically are complicated and vary by platform, which is something I'm keen to fix.)
Paths that don't exist are okay, and that's the zip file. You can choose to put the stdlib into a zip, and it will be found automatically if you name it the default path, but you can also leave it unzipped and reference the directory.
A full walk through on embedding is more than I'm prepared to type on my phone. Hopefully that's enough to get you going for now.
I had the problem and was tinkering with different solutions mentioned here. Since I was running my project from Visual Studio, apparently, I needed to set the environment path inside Visual Studio and not the system path.
Adding a simple PYTHONHOME=PATH\TO\PYTHON\DIR in the project solution\properties\environment solved the problem.
For me this happened when I updated Python 64 bit from 3.6.4 to 3.6.5. It threw some error like "unable to extract python.dll. Do you have permissions."
Pycharm also failed to load interpreter, even though I reloaded it in settings. Running python command gave same error, with and without administrator mode.
Reason
There was error in installation of Python, include folder in python installation directory C:\Users\USERNAME\AppData\Local\Programs\Python\Python36 was missing
Reinstalling Python also dint solve the issue.(Not removal and install)
Solution
Uninstall Python and Install of Python again.
Because running installer was just extracting same files excluding include folder
In my cases, for windows, if you have multiple python versions installed, if PYTHONPATH is pointing to one version the other ones didn't work. I found that if you just remove PYTHONPATH, they all work fine
For those working in Visual Studio simply add the include, Lib and libs directories to the Include Directories and Library Directories under
Projects Properties -> Configuration Properties > VC++ Directories :
For example I have Anaconda3 on my system and working with Visual Studio 2015 This is how the settings looks like (note the Include and Library directories) :
Edit:
As also pointed out by bossi setting PYTHONPATH in your user Environment Variables section seems necessary.
a sample input can be like this (in my case):
C:\Users\Master\Anaconda3\Lib;C:\Users\Master\Anaconda3\libs;C:\Users\Master\Anaconda3\Lib\site-packages;C:\Users\Master\Anaconda3\DLLs
is necessary it seems.
Also, you need to restart Visual Studio after you set up the PYTHONPATH in your user Environment Variables for the changes to take effect.
Also note that :
Make sure the PYTHONHOME environment variable is set to the Python
interpreter you want to use. The C++ projects in Visual Studio rely on
this variable to locate files such as python.h, which are used when
creating a Python extension.
So, for some reason the python dll fails to locate the encodings module. The python.exe executable apparently finds it because it has the expected relative path. Modifying the search path works.
The reason for all of this? Don't know but at least it works. I highly suspect a typo on my part somewhere, that's usually the reason for odd bugs it seems.