Get access to class attributes - python-2.7

Question

import yaml
class Import_Yaml_Setting():
def __init__(self, path):
self.read_yaml(path)
def read_yaml(self, path):
stream = open(path, 'r')
self.settings = yaml.load(stream)
stream.close()
class MasterDef(Import_Yaml_Setting):
def __init__(self, path):
Import_Yaml_Setting.__init__(self, path)
def function_1():
path = 'path_to_settings\\yaml_file.yaml'
MasterDef(path)
def function_2():
MasterDef.settings
if __name__ == '__main__':
function_1()
function_2()
My plan is it to have a class Import_Yaml_Setting which imports settings from a yaml file. The class MasterDef inherits the class Import_Yaml_Setting.
After 'function_1' calls MasterDef in order to import the settings. I want to do this once in my program. After, I just want to get access to the imported settings
without import them again. This should do function_2.
My problem
I don't know how I have to call MasterDef at the first place. If I would create an instance of MasterDef them I wouldn't have access to this instance in function_2.
Also, I get an error that says MasterDef has no attribute settings.
What would be the right way to do this.

Answer 1

There are a few things incorrect, so lets start with the most obvious.
If you have a class MasterDef, calling MasterDef() creates an instance
of that class. If you don't assign that to a variable, that instance will
immediately disappear.
Doing MasterDef.settings later on could work if the class had a
class attribute or method called settings, but in that case you are not accessing
the settings attribute on an instance.
Typical such global settings are passed around, or implemented as a function object that
does the loading only once, or are made into a global variable (as
shown in the following example). Simplified you would do:
from __future__ import print_function, absolute_import, division, unicode_literals
class MasterDef(object):
def __init__(self):
self.settings = dict(some='setting')
master_def = None
def function_1():
global master_def
if master_def is None:
master_def = MasterDef()
def function_2():
print('master_def:', master_def.settings)
if __name__ == '__main__':
function_1()
function_2()
which gives:
master_def: {'some': 'setting'}
A few notes to the above:
If, for whatever reason, you are doing anything new on Python 2.7
make things more Python3 compatible by including the from
__future__ import as indicated. Even if you are just using the
print function (instead of the outdated print statement). It
will make transitioning easier (2.7 goes EOL in 2020)
Again in 2.7 make your base classes a subclass of object, that
makes it e.g. possible to have properties.
By testing that master_def is None you can invoke function_1 multiple
times
You should also be aware that PyYAML load, as is written in its
documentation, can be unsafe when you don't have full control over
your input. There is seldom need to use load() so use safe_load()
or upgrade to my ruamel.yaml package which implements the newer YAML
1.2 standard (released 2009, so there is no excuse for using PyYAML
that still doesn't support that).
As you also seem to be on Windows (assumed from you using \\), consider using raw strings
where you don't need to escape the backslash, using os.path.join(). I am leaving out
your path part in my full example as I am not on Windows:
from __future__ import print_function, absolute_import, division, unicode_literals
import ruamel.yaml
class Import_Yaml_Setting(object):
def __init__(self, path):
self._path = path # stored in case you want to write out the configuration
self.settings = self.read_yaml(path)
def read_yaml(self, path):
yaml = ruamel.yaml.YAML(typ='safe')
with open(path, 'r') as stream:
return yaml.load(stream)
class MasterDef(Import_Yaml_Setting):
def __init__(self, path):
Import_Yaml_Setting.__init__(self, path)
master_def = None
def function_1():
global master_def
path = 'yaml_file.yaml'
if master_def is None:
master_def = MasterDef(path)
def function_2():
print('master_def:', master_def.settings)
if __name__ == '__main__':
function_1()
function_2()
If your YAML file looks like:
example: file
very: simple
the output of the above program will be:
master_def: {'example': 'file', 'very': 'simple'}