Python avoid nesting when checking multiple conditions

Question

I have this python conditions

a=a_foo()
if a==True:
  b=b_foo():
    if b==True:
      c=c_foo()
      if c==True:
         d=d_foo()
      else:
        print('c error')
    else:
      print('b error')
  else:
    print('a error')

The code is working, but if i use this conditions for a-z, the code seems bad.

What a better solution ?

EDIT :

Thanks for comment, i will use if a instead of if a == True

also a_foo, b_foo, c_foo functions is only example, can be function1,func2,funcother,etc

and last, the function also have parameter, example a_foo(p1, p2)

quamrana · Accepted Answer · 2021-01-10T18:11:06.987

3

You just need to list the functions that you want to call. However, you will need some way of identifying which function failed:

funcs = [a_foo,b_foo,c_foo,d_foo]   # add more functions as required

for f in funcs:
   if not f():
        print(f.__name__, "error")
        break

If you want to have different sets of parameters with each function:

funcs = [(a_foo,),(b_foo,b),(c_foo,c,d),(d_foo,d,e,f)]   # add more functions as required

for f,*args in funcs:
   if not f(*args):
        print(f.__name__, "error")
        break

edited Jan 10 '21 at 18:11

answered Jan 10 '21 at 17:27

quamrana

37,849
12
53
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how if each function have different parameter – Anas Fanani Jan 10 '21 at 17:42
this is what i looking for, thanks for answer – Anas Fanani Jan 10 '21 at 18:15

score 2 · Answer 2 · answered Jan 10 '21 at 17:34

You can simply put functions and messages into a list of tuples:

# each element is a tuple with a function to execute and error message when result is False
functions_with_messages = [(a_foo, 'a error'), (b_foo, 'b error'), (c_foo, 'c error')]

for function, error_message in functions_with_messages:
    function_result = function()
    if not function_result:
        print(error_message)
        break  # optional if you want to stop execution of next functions

It would be more idiomatic than the hack-y way of getting function's name with function.__name__. It can be also easily translated into other programming languages.

score 0 · Answer 3 · answered Jan 10 '21 at 17:25

0

Put this in a function and then you can return from it so there's no need to keep nesting.

a = a_foo()
if not a:
    print('a error')
    return

b = b_foo()
if not b:
    print('b error')
    return

answered Jan 10 '21 at 17:25

Charles Duffy

280,126
43
390
441

score -2 · Answer 4 · answered Jan 10 '21 at 17:33

-2

2 line solution here.

from string import ascii_lowercase
[print(i) for i in ascii_lowercase if eval(f'{i}_foo()')]

answered Jan 10 '21 at 17:33

Enes Doğan

29
3

4

It's a nice one-liner but using `eval` is bad in general, see [Why is using eval a bad practive?](https://stackoverflow.com/questions/1832940/why-is-using-eval-a-bad-practice). – asikorski Jan 10 '21 at 17:37
I know but still it's a one-liner. – Enes Doğan Jan 10 '21 at 17:41
4

It might be a one-liner, but it is not a good solution. Just because you can do a thing, doesn't mean you should do a thing. – Trenton McKinney Jan 10 '21 at 20:29

Python avoid nesting when checking multiple conditions

4 Answers4