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Using command line arguments with argv

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Whenever a Python script is invoked from the command line, the user may supply additional command line arguments which will be passed on to the script. These arguments will be available to the programmer from the system variable sys.argv (“argv” is a traditional name used in most programming languages, and it means “argument vector”).

By convention, the first element in the sys.argv list is the name of the Python script itself, while the rest of the elements are the tokens passed by the user when invoking the script. 

# cli.py
import sys
print(sys.argv)

$ python cli.py
=> ['cli.py']

$ python cli.py fizz
=> ['cli.py', 'fizz']

$ python cli.py fizz buzz
=> ['cli.py', 'fizz', 'buzz']

Here’s another example of how to use argv. We first strip off the initial element of sys.argv because it contains the script’s name. Then we combine the rest of the arguments into a single sentence, and finally print that sentence prepending the name of the currently logged-in user (so that it emulates a chat program). 

import getpass
import sys

words = sys.argv[1:]
sentence = " ".join(words)
print("[%s] %s" % (getpass.getuser(), sentence))

The algorithm commonly used when “manually” parsing a number of non-positional arguments is to iterate over the sys.argv list. One way is to go over the list and pop each element of it: 

# reverse and copy sys.argv
argv = reversed(sys.argv)
# extract the first element
arg = argv.pop()
# stop iterating when there's no more args to pop()
while len(argv) > 0:
    if arg in ('-f', '--foo'):
        print('seen foo!')
    elif arg in ('-b', '--bar'):
        print('seen bar!')
    elif arg in ('-a', '--with-arg'):
        arg = arg.pop()
        print('seen value: {}'.format(arg))
    # get the next value
    arg = argv.pop()
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Parsing Command Line Arguments:
* Parsing Command Line arguments
* Hello world in argparse
* Using command line arguments with argv
* Setting mutually exclusive arguments with argparse
* Basic example with docopt
* Custom parser error message with argparse
* Conceptual grouping of arguments with argparse.add argument group
* Advanced example with docopt and docopt dispatch
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116 List destructuring
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148 Defining functions with list arguments
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154 Audio
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156 queue module
157 ijson
158 webbrowser module
159 base64 module
160 Flask
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162 Sockets and Message Encryption / Decryption
163 pygame
164 Input Subset and Output External Data Files using Pandas
165 hashlib
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168 Creating a Windows Service
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170 configparser
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172 Optical Character Recognition OCR
173 Python Data Types
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175 Generating graphs
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177 Functional Programming
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179 sys module
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181 virtualenvwrapper on Windows
182 Python Requests Post
183 Plotting with Matplotlib
184 Python Lex-Yacc
185 pyaudio
186 shelve
187 pip and PyPI Package Manager
188 Writing to CSV from String or List
189 Raise Custom Errors Exceptions
190 Using loops within functions
191 Contributors