Question

I have a situation where I would like to conditionally slice a string from the
reported position of an ‘@’ symbol; the condition being: slice the string if
the ‘@’ is there, else leave it untouched. I thought up two ways, one using a
function, the other using an inline conditional expression. Which method is the
most Pythonic?

Using a function

>>> def slice_from_at(inp):
...     res = inp.find('@')
...     if res == -1:
...         return None
...     else:
...         return res     
>>> c = 'agent_address@agent_address'
>>> c[:slice_from_at(c)]
... 'agent_address'

Using an inline conditional expression

>>> c = 'agent_address@agent_address'
>>> c[:None if c.find('@') == -1 else c.find('@')]
... 'agent_address'

Although using the inline conditional expression is more terse and, some may
argue more economical – is the function method is more Pythonic because it more
readable?

Answer 1

Not only is a function more readable, it is also reusable.

The inline expression may call c.find('@') twice, which is inefficient.

As Useless has mentioned in the comments, there are already built in functions to do this; you really don’t need to define your own function in this case:

agent,_,address = c.partition('@')

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By the way, a callback is a function that is passed in as an argument and called later. You don’t have a callback since it is not being called later. I think it should just be called a function.