Does Python have an argc argument?

Question

I have written the same program (open text file and display contents) in C and C++. Now am doing the same in Python (on a Linux machine).

In the C programs I used the code:

if (argc != 2) {
    /* exit program */
}

Question: What is used in Python to check the number of arguments

#!/usr/bin/python
import sys
try:
    in_file = open(sys.argv[1], "r")
except:
    sys.exit("ERROR. Did you make a mistake in the spelling")
text = in_file.read()
print text
in_file.close()

Current output:

./python names.txt = Displays text file (correct)
./python nam = error message: stated from the sys.ext line (correct)
./python = error message: stated from the sys.ext line (wrong: want it to be a
separate error message stating *no file name input*)

Asked By: Dan1676

||

Source

Answer 1

In python a list knows its length, so you can just do len(sys.argv) to get the number of elements in argv.

Answered By: sepp2k

Answer 2

I often use a quick-n-dirty trick to read a fixed number of arguments from the command-line:

[filename] = sys.argv[1:]

in_file = open(filename)   # Don't need the "r"

This will assign the one argument to filename and raise an exception if there isn’t exactly one argument.

Answered By: Marcelo Cantos

Answer 3

dir(sys) says no. len(sys.argv) works, but in Python it is better to ask for forgiveness than permission, so

#!/usr/bin/python
import sys
try:
    in_file = open(sys.argv[1], "r")
except:
    sys.exit("ERROR. Can't read supplied filename.")
text = in_file.read()
print(text)
in_file.close()

works fine and is shorter.

If you’re going to exit anyway, this would be better:

#!/usr/bin/python
import sys
text = open(sys.argv[1], "r").read()
print(text)

I’m using print() so it works in 2.7 as well as Python 3.

Answered By: Cees Timmerman

Answer 4

You’re better off looking at argparse for argument parsing.

http://docs.python.org/dev/library/argparse.html

Just makes it easy, no need to do the heavy lifting yourself.

Answered By: Nickle

Does Python have an argc argument?

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