Flag control variable

[Peter Otten]

luke.geelen at gmail.com wrote:

> well i'm trying something else but no luck :
> 
> #!bin/bash/python

Hm.

> import sys
> import os

For debugging purposes put the line

print sys.argv

here to see what arguments are passed to the script. When you type

$ python script.py 2 * 2

in the shell the "*" sign is replaced with all items in the current 
directory. To avoid that you have to escape, i. e. prepend a backslash:

$ python script.py 2 \* 2

To illustrate:

$ touch one two three
$ ls
one  three  two
$ python -c 'import sys; print sys.argv' 2 + 2
['-c', '2', '+', '2']
$ python -c 'import sys; print sys.argv' 2 * 2
['-c', '2', 'one', 'three', 'two', '2']
$ python -c 'import sys; print sys.argv' 2 \* 2
['-c', '2', '*', '2']

> a = int(sys.argv[1])
> sign = (sys.argv[2])
> b = int(sys.argv[3])
> 
> if sign == '+':
>   sum = a + b
>   print a, sign, b, "=", a + b
>   command1 = "sudo mpg321 
>   'http://translate.google.com/translate_tts?tl=en&q=%s_plus%s_equals%s'"
>   % (a, b, sum) os.system (command1)
> 
> elif sign == "*":
>   sum = a * b
>   print a, sign, b, "=", a * b
>   command1 = "sudo mpg321 
>   'http://translate.google.com/translate_tts?tl=en&q=%s_times%s_equals%s'"
>   % (a, b, sum)
> 
> when using * i get
> 
> Traceback (most recent call last):
>   File "./math+.py", line 6, in <module>
>     b = int(sys.argv[3])
> ValueError: invalid literal for int() with base 10:
> 'Adafruit-Raspberry-Pi-Python-Code'
> 
> i don't understand why b is a problem, it works fine with +