import sys
def Hello(name):
name = name + '!!!'
print 'Hello' , name
def main():
Hello(sys.argv[1])
if __name__ == '__main__':
main()
Here is the error
Traceback (most recent call last):
File "D:\pythonPractice\firstPython.py", line 13, in <module>
main()
File "D:\pythonPractice\firstPython.py", line 9, in main
Hello(sys.argv[1])
IndexError: list index out of range
I have also tried sys.argv[2] but error remains
First things first, I think the code you originally posted (with Hello(sys.argv[0])) is not what you actually have. It doesn't match the error, which states sys.argv[1], so what you probably have is:
def main():
Hello(sys.argv[1])
As to the error then, it's because you haven't provided an argument when running. You need to do so, such that sys.argv[1] exists:
python helloprog Pax
You would find a more robust main as:
def main():
if len(sys.argv) < 2:
Hello("whoever you are")
else:
Hello(sys.argv[1])
which will detect when you haven't provided an argument, and use a suitable default rather than raising an exception.
Have you used
sys.argv[0]
Since this returns a list , you may not have elements >1
Related
I have to monitor an XML file being written by a tool running all the day. But the XML file is properly completed and closed only at the end of the day.
Same constraints as XML stream processing:
Parse an incomplete XML file on-the-fly and trigger actions
Keep track of the last position within the file to avoid processing it again from the beginning
On answer of Need to read XML files as a stream using BeautifulSoup in Python, slezica suggests xml.sax, xml.etree.ElementTree and cElementTree. But no success with my attempts to use xml.etree.ElementTree and cElementTree. There are also xml.dom, xml.parsers.expat and lxml but I do not see support for "on-the-fly parsing".
I need more obvious examples...
I am currently using Python 2.7 on Linux, but I will migrate to Python 3.x => please also provide tips on new Python 3.x features. I also use watchdog to detect XML file modifications => Optionally, reuse the watchdog mechanism. Optionally support also Windows.
Please provide easy to understand/maintain solutions. If it is too complex, I may just use tell()/seek() to move within the file, use stupid text search in the raw XML and finally extract the values using basic regex.
XML sample:
<dfxml xmloutputversion='1.0'>
<creator version='1.0'>
<program>TCPFLOW</program>
<version>1.4.6</version>
</creator>
<configuration>
<fileobject>
<filename>file1</filename>
<filesize>288</filesize>
<tcpflow packets='12' srcport='1111' dstport='2222' family='2' />
</fileobject>
<fileobject>
<filename>file2</filename>
<filesize>352</filesize>
<tcpflow packets='12' srcport='3333' dstport='4444' family='2' />
</fileobject>
<fileobject>
<filename>file3</filename>
<filesize>456</filesize>
...
...
First test using SAX failed:
import xml.sax
class StreamHandler(xml.sax.handler.ContentHandler):
def startElement(self, name, attrs):
print 'start: name=', name
def endElement(self, name):
print 'end: name=', name
if name == 'root':
raise StopIteration
if __name__ == '__main__':
parser = xml.sax.make_parser()
parser.setContentHandler(StreamHandler())
with open('f.xml') as f:
parser.parse(f)
Shell:
$ while read line; do echo $line; sleep 1; done <i.xml >f.xml &
...
$ ./test-using-sax.py
start: name= dfxml
start: name= creator
start: name= program
end: name= program
start: name= version
end: name= version
Traceback (most recent call last):
File "./test-using-sax.py", line 17, in <module>
parser.parse(f)
File "/usr/lib64/python2.7/xml/sax/expatreader.py", line 107, in parse
xmlreader.IncrementalParser.parse(self, source)
File "/usr/lib64/python2.7/xml/sax/xmlreader.py", line 125, in parse
self.close()
File "/usr/lib64/python2.7/xml/sax/expatreader.py", line 220, in close
self.feed("", isFinal = 1)
File "/usr/lib64/python2.7/xml/sax/expatreader.py", line 214, in feed
self._err_handler.fatalError(exc)
File "/usr/lib64/python2.7/xml/sax/handler.py", line 38, in fatalError
raise exception
xml.sax._exceptions.SAXParseException: report.xml:15:0: no element found
Since yesterday I found the Peter Gibson's answer about the undocumented xml.etree.ElementTree.XMLTreeBuilder._parser.EndElementHandler.
This example is similar to the other one but uses xml.etree.ElementTree (and watchdog).
It does not work when ElementTree is replaced by cElementTree :-/
import time
import watchdog.events
import watchdog.observers
import xml.etree.ElementTree
class XmlFileEventHandler(watchdog.events.PatternMatchingEventHandler):
def __init__(self):
watchdog.events.PatternMatchingEventHandler.__init__(self, patterns=['*.xml'])
self.xml_file = None
self.parser = xml.etree.ElementTree.XMLTreeBuilder()
def end_tag_event(tag):
node = self.parser._end(tag)
print 'tag=', tag, 'node=', node
self.parser._parser.EndElementHandler = end_tag_event
def on_modified(self, event):
if not self.xml_file:
self.xml_file = open(event.src_path)
buffer = self.xml_file.read()
if buffer:
self.parser.feed(buffer)
if __name__ == '__main__':
observer = watchdog.observers.Observer()
event_handler = XmlFileEventHandler()
observer.schedule(event_handler, path='.')
try:
observer.start()
while True:
time.sleep(10)
finally:
observer.stop()
observer.join()
While the script is running, do not forget to touch one XML file, or simulate the on-the-fly writing using this one line script:
while read line; do echo $line; sleep 1; done <in.xml >out.xml &
For information, the xml.etree.ElementTree.iterparse does not seem to support a file being written. My test code:
from __future__ import print_function, division
import xml.etree.ElementTree
if __name__ == '__main__':
context = xml.etree.ElementTree.iterparse('f.xml', events=('end',))
for action, elem in context:
print(action, elem.tag)
My output:
end program
end version
end creator
end filename
end filesize
end tcpflow
end fileobject
end filename
end filesize
end tcpflow
end fileobject
end filename
end filesize
Traceback (most recent call last):
File "./iter.py", line 9, in <module>
for action, elem in context:
File "/usr/lib64/python2.7/xml/etree/ElementTree.py", line 1281, in next
self._root = self._parser.close()
File "/usr/lib64/python2.7/xml/etree/ElementTree.py", line 1654, in close
self._raiseerror(v)
File "/usr/lib64/python2.7/xml/etree/ElementTree.py", line 1506, in _raiseerror
raise err
xml.etree.ElementTree.ParseError: no element found: line 20, column 0
Three hours after posting my question, no answer received. But I have finally implemented the simple example I was looking for.
My inspiration is from saaj's answer and is based on xml.sax and watchdog.
from __future__ import print_function, division
import time
import watchdog.events
import watchdog.observers
import xml.sax
class XmlStreamHandler(xml.sax.handler.ContentHandler):
def startElement(self, tag, attributes):
print(tag, 'attributes=', attributes.items())
self.tag = tag
def characters(self, content):
print(self.tag, 'content=', content)
class XmlFileEventHandler(watchdog.events.PatternMatchingEventHandler):
def __init__(self):
watchdog.events.PatternMatchingEventHandler.__init__(self, patterns=['*.xml'])
self.file = None
self.parser = xml.sax.make_parser()
self.parser.setContentHandler(XmlStreamHandler())
def on_modified(self, event):
if not self.file:
self.file = open(event.src_path)
self.parser.feed(self.file.read())
if __name__ == '__main__':
observer = watchdog.observers.Observer()
event_handler = XmlFileEventHandler()
observer.schedule(event_handler, path='.')
try:
observer.start()
while True:
time.sleep(10)
finally:
observer.stop()
observer.join()
While the script is running, do not forget to touch one XML file, or simulate the on-the-fly writing using the following command:
while read line; do echo $line; sleep 1; done <in.xml >out.xml &
I am trying to debug python code, I want to pin point the line number in which error occurs. As per the posts found asked here the code gives the line no of the function being called. eg
if __name__ == '__main__':
try:
foo()
except:
<the code to print line no when error occurs>
But it gives me the line no of foo(),
Please help to find the exact line no in which error occurs.
Thanks,
You have to use the third return value of sys.exc_info() they call exc_tb in your example. Instead of using exc_tb.tb_lineno, you can browse the traceback object using traceback.extract_tb(exc_tb). The repr look like :
*** extract_tb:
[('<doctest...>', 10, '<module>', 'lumberjack()'),
('<doctest...>', 4, 'lumberjack', 'bright_side_of_death()'),
('<doctest...>', 7, 'bright_side_of_death', 'return tuple()[0]')]
I suppose the line you are looking for is the last line of the structure. I haven't tested but this should do :
import sys, os, traceback
try:
raise NotImplementedError("No error")
except Exception as e:
exc_type, exc_obj, exc_tb = sys.exc_info()
tb = traceback.extract_tb(exc_tb)[-1]
print(exc_type, tb[2], tb[1])
I was reading a similar question Returning error string from a function in python. While I experimenting to create something similar in an Object Oriented programming so I could learn a few more things I got lost.
I am using Python 2.7 and I am a beginner on Object Oriented programming.
I can not figure out how to make it work.
Sample code checkArgumentInput.py:
#!/usr/bin/python
__author__ = 'author'
class Error(Exception):
"""Base class for exceptions in this module."""
pass
class ArgumentValidationError(Error):
pass
def __init__(self, arguments):
self.arguments = arguments
def print_method(self, input_arguments):
if len(input_arguments) != 3:
raise ArgumentValidationError("Error on argument input!")
else:
self.arguments = input_arguments
return self.arguments
And on the main.py script:
#!/usr/bin/python
import checkArgumentInput
__author__ = 'author'
argsValidation = checkArgumentInput.ArgumentValidationError(sys.argv)
if __name__ == '__main__':
try:
result = argsValidation.validate_argument_input(sys.argv)
print result
except checkArgumentInput.ArgumentValidationError as exception:
# handle exception here and get error message
print exception.message
When I am executing the main.py script it produces two blank lines. Even if I do not provide any arguments as input or even if I do provide argument(s) input.
So my question is how to make it work?
I know that there is a module that can do that work for me, by checking argument input argparse but I want to implement something that I could use in other cases also (try, except).
Thank you in advance for the time and effort reading and replying to my question.
OK. So, usually the function sys.argv[] is called with brackets in the end of it, and with a number between the brackets, like: sys.argv[1]. This function will read your command line input. Exp.: sys.argv[0] is the name of the file.
main.py 42
In this case main.py is sys.argv[0] and 42 is sys.argv[1].
You need to identifi the string you're gonna take from the command line.
I think that this is the problem.
For more info: https://docs.python.org/2/library/sys.html
I made some research and I found this useful question/ answer that helped me out to understand my error: Manually raising (throwing) an exception in Python
I am posting the correct functional code under, just in case that someone will benefit in future.
Sample code checkArgumentInput.py:
#!/usr/bin/python
__author__ = 'author'
class ArgumentLookupError(LookupError):
pass
def __init__(self, *args): # *args because I do not know the number of args (input from terminal)
self.output = None
self.argument_list = args
def validate_argument_input(self, argument_input_list):
if len(argument_input_list) != 3:
raise ValueError('Error on argument input!')
else:
self.output = "Success"
return self.output
The second part main.py:
#!/usr/bin/python
import sys
import checkArgumentInput
__author__ = 'author'
argsValidation = checkArgumentInput.ArgumentLookupError(sys.argv)
if __name__ == '__main__':
try:
result = argsValidation.validate_argument_input(sys.argv)
print result
except ValueError as exception:
# handle exception here and get error message
print exception.message
The following code prints: Error on argument input! as expected, because I violating the condition.
Any way thank you all for your time and effort, hope this answer will help someone else in future.
I am using grpc with protobuf 2.6.1 in python 2.7, and when I run my client side code, I have the following errors:
Traceback (most recent call last):
File "debate_client.py", line 31, in <module>
run_client()
File "debate_client.py", line 17, in run_client
reply = stub.Answer(debate_pb2.AnswerRequest(question=question, timeout=timeout), 30)
File "/Users/elaine/Desktop/gitHub/grpc/python2.7_virtual_environment/lib/python2.7/site-packages/grpc/framework/crust/implementations.py", line 73, in __call__
protocol_options, metadata, request)
File "/Users/elaine/Desktop/gitHub/grpc/python2.7_virtual_environment/lib/python2.7/site-packages/grpc/framework/crust/_calls.py", line 109, in blocking_unary_unary
return next(rendezvous)
File "/Users/elaine/Desktop/gitHub/grpc/python2.7_virtual_environment/lib/python2.7/site-packages/grpc/framework/crust/_control.py", line 412, in next
raise self._termination.abortion_error
grpc.framework.interfaces.face.face.RemoteError: RemoteError(code=StatusCode.UNKNOWN, details="")
Here is my client side code:
from grpc.beta import implementations
import debate_pb2
import sys
def run_client():
params = sys.argv
print params
how = params[1]
question = params[2]
channel = implementations.insecure_channel('localhost', 29999)
stub = debate_pb2.beta_create_Candidate_stub(channel)
if how.lower() == "answer":
timeout = int(params[3])
reply = stub.Answer(debate_pb2.AnswerRequest(question=question, timeout=timeout), 30)
elif how.lower() == "elaborate":
blah = params[3:len(sys.argv)]
for i in range(0, len(blah)):
blah[i] = int(blah[i])
reply = stub.Elaborate(debate_pb2.ElaborateRequest(topic=question, blah_run=blah), 30)
if reply is None:
print "No comment"
else:
print reply.answer
if __name__ == "__main__":
run_client()
And here is my server side code:
import debate_pb2
import consultation_pb2
import re
import random
from grpc.beta import implementations
class Debate(debate_pb2.BetaCandidateServicer):
def Answer(self, request, context=None):
#Answer implementation
def Elaborate(self, request, context=None):
#Elaborate implementation
def run_server():
server = debate_pb2.beta_create_Candidate_server(Debate())
server.add_insecure_port('localhost:29999')
server.start()
if __name__ == "__main__":
run_server()
Any idea where the remote error comes from? Thank you so much!
Hello Elaine and thank you for trying out gRPC Python.
Nothing leaps out at me as an obvious smoking gun, but a couple of things I see are:
gRPC Python isn't known to work with protobuf 2.6.1. Have you tried working with the very latest protobuf release (3.0.0a3 at this time)?
context isn't an optional keyword parameter in servicer methods; it's a required, positional parameter. Does dropping =None from your servicer method implementations effect any change?
The same happened to me just now, and I figured out why.
Make sure the messages in your proto definition and the message in your implementations match the format.
For example, my Response message had a message= param in my python server, but not in my proto definition.
I think your function implementations should be outside class Debate or might be your functions are not correctly implemented to give the desired result.
I faced a similar error because my functions were inside the class but moving it outside the class fixed it.
I've written one small python script to fix the checksum of L3-4 protocols using scapy. When I'm running the script it is not taking command line argument or may be some other reason it is not generating the fix checksum pcap. I've verified the rdpcap() from scapy command line it is working file using script it is not getting executed. My program is
import sys
import logging
logging.getLogger("scapy").setLevel(1)
try:
from scapy.all import *
except ImportError:
import scapy
if len(sys.argv) != 3:
print "Usage:./ChecksumFixer <input_pcap_file> <output_pcap_file>"
print "Example: ./ChecksumFixer input.pcap output.pcap"
sys.exit(1)
#------------------------Command Line Argument---------------------------------------
input_file = sys.argv[1]
output_file = sys.argv[2]
#------------------------Get The layer and Fix Checksum-------------------------------
def getLayer(p):
for paktype in (scapy.IP, scapy.TCP, scapy.UDP, scapy.ICMP):
try:
p.getlayer(paktype).chksum = None
except: AttributeError
pass
return p
#-----------------------FixPcap in input file and write to output fi`enter code here`le----------------
def fixpcap():
paks = scapy.rdpcap(input_file)
fc = map(getLayer, paks)
scapy.wrpcap(output_file, fc)
The reason your function is not executed is that you're not invoking it. Adding a call to fixpcap() at the end of your script shall fix this issue.
Furthermore, here are a few more corrections & suggestions:
The statement following except Exception: should be indented as well, as follows:
try:
from scapy.all import *
except ImportError:
import scapy
Use argparse to parse command-line arguments.
Wrap your main code in a if __name__ == '__main__': block.