Eli Bendersky Eli Bendersky - 3 months ago 12
Python Question

Python style: multiple-line conditions in IFs

Sometimes I break long conditions in IFs to several lines. The most obvious way to do this is:

if (cond1 == 'val1' and cond2 == 'val2' and
cond3 == 'val3' and cond4 == 'val4'):
do_something


Isn't very very appealing visually, because the action blends with the conditions. However, it is the natural way using correct Python indentation of 4 spaces.

For the moment I'm using:

if ( cond1 == 'val1' and cond2 == 'val2' and
cond3 == 'val3' and cond4 == 'val4'):
do_something


But this isn't very pretty. :-)

Can you recommend an alternative way ?

Answer

You don't need to use 4 spaces on your second conditional line. Maybe use:

if (cond1 == 'val1' and cond2 == 'val2' and 
       cond3 == 'val3' and cond4 == 'val4'):
    do_something

Also, don't forget the whitespace is more flexible than you might think:

if (   
       cond1 == 'val1' and cond2 == 'val2' and 
       cond3 == 'val3' and cond4 == 'val4'
   ):
    do_something
if    (cond1 == 'val1' and cond2 == 'val2' and 
       cond3 == 'val3' and cond4 == 'val4'):
    do_something

Both of those are fairly ugly though.

Maybe lose the brackets (the Style Guide discourages this though)?

if cond1 == 'val1' and cond2 == 'val2' and \
   cond3 == 'val3' and cond4 == 'val4':
    do_something

This at least gives you some differentiation.

Or even:

if cond1 == 'val1' and cond2 == 'val2' and \
                       cond3 == 'val3' and \
                       cond4 == 'val4':
    do_something

I think I prefer:

if cond1 == 'val1' and \
   cond2 == 'val2' and \
   cond3 == 'val3' and \
   cond4 == 'val4':
    do_something

Here's the Style Guide, which (since 2010) recommends using brackets.

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