Question

I am analyzing the repo script from Google (instructions at http://source.android.com/source/downloading.html)

The repo script is written in Python. There is a part in there that says:

if sys.argv[-1] =='#%s' % magic

Can somebody explain semantically what that line means? I am a bit rusty on my Python. The entire block of code for this is:

magic='--calling-python-from-/bin/sh--'
"""exec" python -E "$0" "$@" """#$magic"
if __name__ == '__main__':
    import sys
    if sys.argv[-1] =='#%s' % magic:
        del sys.argv[-1]

Answer 1

One piece at the time:

• sys.argv holds the list of command line arguments passed to a Python script. Meaning that sys-argv[-1] is the last argument.
• '#%s' % magic. The % formats your string, which means the where you see %s there’s going to be the value of magic (if magic is not a string it will be converted: str(magic)). In your code that string is going to be: '#--calling-python-from-/bin/sh--'.
• del sys.argv[-1]. This is self-explainatory: means that the last value of the list sys.argv is going to be removed.

All together it means that: if the last command line argument is #--calling-python-from-/bin/sh-- that argument is going to be removed from sys.argv.