Change conditions using loop and array in python

Question

i have and old script in python, where in

if __name__ == '__main__': <br>

We call arguments of functions. And if it argument equals some string we should call function. Old code.

if sys.argv[1] == 'add':
    sys.exit(add(db, usr))
if sys.argv[1] == 'rem':
    sys.exit(rem(db, usr))
if sys.argv[1] == 'rmusr':
    sys.exit(rmusr(db, usr))

At the first time, i thought about "switch case", but how i find out, python does not have it. And i tried to loop and array. Can i use it on this ? Sorry, i started learn python, 2 hours ago. But it is very interesting, and i hope, that you can help me.

 actions = ['add','rem','rmusr']
    for a in actions:
    if sys.argv[1] == 'a':
        sys.exit(a(db, usr))

Is it correct ? How i find out, we should not call variables with "$". Please help.

The line if sys.argv[1] == 'a': compares the user input to the character a. I don't think this is what you want. Try removing the single quotes so that you compare argv[1] to the value of the variable a, not the character 'a'. — FCo
– FCo, Commented Apr 19, 2017 at 21:19

Thierry Lathuille · Accepted Answer · 2017-04-19 21:12:55Z

1

Use a dictionary:

actions = {'add': add, 'rem': rem, 'rmusr': rmusr}

try:
    sys.exit(actions[sys.argv[1]](db, usr))
except KeyError:
   pass
   # or whatever you need to do for an invalid action

answered Apr 19, 2017 at 21:12

Thierry Lathuille

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brianpck · Accepted Answer · 2017-04-19 21:10:17Z

0

You can add the functions to the dictionary and then use the user-input string to retrieve the function:

actions = {
    'add': add,
    'rem': rem,
    'rmusr': rmusr,
}

action = sys.argv[1]

if action in actions:
    sys.exit(actions[action](db, usr))

answered Apr 19, 2017 at 21:10

brianpck

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2 Comments

Piduna Over a year ago

but what about my way ? it should not work ? if i want to use loop ?

brianpck Over a year ago

Your example mixes up the function variable (a) with a similar string ('a'): they're not the same. There's no need to add a loop, since the in operator in my example does all the checking you need.

0xMH · Accepted Answer · 2017-04-19 21:57:42Z

0

your code could be right but there is a typo on it.

actions = ['add','rem','rmusr']
for a in actions:
    if sys.argv[1] == 'a':
        sys.exit(a(db, usr))

I think It's better using in:

actions = ['add','rem','rmusr']
if sys.argv[1] in actions:
    sys.exit(sys.argv[1](db, usr))

answered Apr 19, 2017 at 21:57

0xMH

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