execute python script with function from command line, Linux

Question

I have my python file called convertImage.py and inside the file I have a script that converts an image to my liking, the entire converting script is set inside a function called convertFile(fileName)

Now my problem is I need to execute this python script from the linux command line while passing the convertFile(fileName) function along with it.

example:

 linux user$: python convertImage.py convertFile(fileName)

This should execute the python script passing the appropriate function.

example:

def convertFile(fileName):
 import os, sys
 import Image
 import string
 splitName = string.split(fileName, "_")
 endName = splitName[2]
 splitTwo = string.split(endName, ".")
 userFolder = splitTwo[0]
 imageFile = "/var/www/uploads/tmp/"+fileName
 ...rest of the script...
 return

What is the right way to execute this python script and properly pass the file name to the function from the liunx command line?

Thank in advanced

• JBernardo: there's no such thing. Parse the sys.argv list and choose the right action. Check argparse the module
• Cascabel: As mentioned by S.Lott, <program> <subcommand> <command arguments> is a very common style. It's best for the user to have command names, not knowledge of the internal implementation. And using parentheses (which require escaping in bash) as a required part of your syntax is just mean.
• knittledan: The parentheses were only for example reasons but I appreciated all the help and got it to work using sys.argv
• S.Lott: @knittledan: sys.argv is -- usually -- a poor choice. Notice that the answers all specifically recommended avoiding this.

Answer 1

This

if __name__ == "__main__":
 command= " ".join( sys.argv[1:] )
 eval( command )

This will work. But it's insanely dangerous.

You really need to think about what your command-line syntax is. And you need to think about why you're breaking the long-established Linux standards for specifying arguments to a program.

For example, you should consider removing the useless ()'s in your example. Make it this, instead.

python convertImage.py convertFile fileName

Then, you can -- with little work -- use argparse to get the command ("convertFile") and the arguments ("fileName") and work within the standard Linux command line syntax.

function_map = { 
 'convertFile': convertFile,
 'conv': convertFile,
}
parser = argparse.ArgumentParser()
parser.add_argument( 'command', nargs=1 )
parser.add_argument( 'fileName', nargs='+' )
args= parser.parse_args()
function = function_map[args.command]
function( args.fileName )

• Thomas: Good combination of briefly answering X by mostly addressing Y
• Helk: @S.Lott What is the purpose of the function_map dict here? Why does it have two keys for the command?
• Timo: If I have several functions, I need to have several function_maps?

Answer 2

Quick and dirty way:

linux user$: python convertImage.py convertFile fileName

and then in convertImage.py

if __name__ == '__main__':
 import sys
 function = getattr(sys.modules[__name__], sys.argv[1])
 filename = sys.argv[2]
 function(filename)

A more sophisticated approach would use argparse (for 2.7 or 3.2+) or optparse.

Answer 3

Create a top-level executable part of your script that parses command-line argument(s) and then pass it to your function in a call, like so:

import os, sys
#import Image
import string
def convertFile(fileName):
 splitName = string.split(fileName, "_")
 endName = splitName[2]
 splitTwo = string.split(endName, ".")
 userFolder = splitTwo[0]
 imageFile = "/var/www/uploads/tmp/"+fileName
 print imageFile # (rest of the script)
 return
if __name__ == '__main__':
 filename = sys.argv[1]
 convertFile(filename)

Then, from a shell,

$ convertImage.py the_image_file.png
/var/www/uploads/tmp/the_image_file.png

• Nick Perkins: does this require a hashbang?
• Timo: This answer shows valid code but does not answer the question. OP asks how to call the function from cmd. Your example calls the argument from cmd.