How To Use sys.argv[] In Python

sys.argv[] is used to get python command line arguments. sys.argv[0] ‘s value is the file path of the python source code file that is running. For example, if you run python test_sys_arg.pyin a terminal, then sys.argv[0]‘s value is test_sys_arg.py. This article will give you two example about how to use sys.argv[] to get command line arguments in python source code.

1. sys.argv[] Example.

Below python file will print out all elements in sys.argv[] list.

1. Save below code in file test_sys_arg.py file.

   # first import built-in sys module.
   import sys
   
   # get command line argument length.
   argv_len = len(sys.argv)
   
   print('there are ' + str(argv_len) + ' arguments.')
   # loop in all arguments.
   for i in range(argv_len):
     tmp_argv = sys.argv[i]
   
     # print out argument index and value.
     print(str(i))
   
     print(tmp_argv)
   
     print('argv ' + str(i) + ' = ' + tmp_argv)

2. Open a terminal and goto above python file sved directory, then run python test_sys_arg.pylike below.

   C:\WorkSpace>python test_sys_arg.py test
   there are 2 arguments.
   0
   test_sys_arg.py
   argv 0 = test_sys_arg.py
   1
   test
   argv 1 = test

2. Read File Example.

Below example will read file content and print it in console, and the file name is passed from the sys.argv[] arguments.

1. Save below python source code in file test_sys_arg.py file.

   import sys
   
   ''' This function will read out a file content and print the content to standard output.'''
   def read_file(file_name):
   
     # open file object use python with statement.
     with open(file_name) as file:
   
       # loop in the file and read each line.
       while True:
         line = file.readline()
   
         if len(line) == 0:
   
           break
   
         print(line)
   
       # print a separator line when read out all file content.
       print('******************* read file ' + file_name + ' end ***************************')
   
   # get argv length.
   argv_len = len(sys.argv)
   
   # loop in the python command arguments list, _ is a local variable which will be dropped after use.
   for _ in range(argv_len):
     
     # the first python command argument is this .py file it's self.
     if(_ >= 0):
   
       # print out argument info.
       print('Argument ' + str(_ + 1) + ' : ' + sys.argv[_])
   
       read_file(sys.argv[_])

2. Create a file text.txt and input some text data. Save it in the same folder of test_sys_arg.py file.
3. Open a terminal and goto above python file sved directory, then run python test_sys_arg.py test.txtlike below.

   C:\WorkSpace>python test_sys_arg.py test.txt
   Argument 1 : test_sys_arg.py
   ......
   ......
   ******************* read file test_sys_arg.py end ***************************
   Argument 2 : test.txt
   ......
   ......
   ******************* read file test.txt end ***************************