Python Function Return

Question

If I want to return more that one variable from a function in Python I have been doing the following:

def foo():
    firstName = 'Bob'
    lastName = 'Jones'
    return [firstName, lastName]

Then if I wanted to find only the first name I would do this

[firstName, dummy] = foo()

However, say I initially had the function

def fooInitial():
    firstName = 'Bob'
    return firstName

and I called this from many parts of my code, if I wanted to add the lastName as another output the way I have been doing, I would have to change everywhere else in my code that was calling it.

Is there a way to do something similar to Matlab where calling a = foo() gives me the first name (not the first and last in a list) and [a,b]=foo() gives me the first and last?

Add to your function argument with default value == False and if argument True return [firstName, lastName] and if False return firstName — Sergey Miryanov
– Sergey Miryanov, Commented Aug 9, 2013 at 10:34

Martijn Pieters · Accepted Answer · 2013-08-09 10:34:37Z

6

No, there isn't. You are better of either changing all the code calling fooInitial(), or by adding a different method that returns the two parameters and have fooInitial() use that method:

def barInitial():
    first_name, last_name = 'Bob', 'Jones'
    return first_name, last_name

def fooInitial():
    return barInitial()[0]

Note that you can just return a tuple instead of a list too; tuples only require a comma to define so the syntax is lighter (no need for square brackets). You can do the same when unpacking the returned value:

first_name, last_name = barInitial()

answered Aug 9, 2013 at 10:34

Martijn Pieters

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3 Comments

Jon Clements Over a year ago

A namedtuple is probably not a bad idea - going on the returning multiple values part of the OP... (just can't be bothered to write an answer for it)

rwolst Over a year ago

Yes, I like this. Changing the name of the initial function seems the best and easiest thing to do. Thanks!

tom Over a year ago

@MartijnPieters I agree with all of your answer except for the first three words.

Aaron Barclay · Accepted Answer · 2013-08-09 12:23:27Z

1

You could do this:

def foo(last=None):
    # current behaviour, change no code
    If not last:
        return 'bob'

    # new behaviour return first and last list
    return ['bob', 'jones']

The addition of the named keyword with a default argument gives you your current behaviour for code you don't want to change, and for new code where you want first and last returned you would use

first, last = foo(last=true)

answered Aug 9, 2013 at 12:23

Aaron Barclay

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Comments

tom · Accepted Answer · 2013-08-09 10:58:18Z

0

It is possible, but I don't recommend it.

# WARNING: Breaks iteration over chars

class StrOrPair(str):
    def __new__(cls, name, lastname):
        return str.__new__(cls, name)

    def __init__(self, name, lastname):
        str.__init__(self, name)
        self.lastname = lastname

    # __iter__ is used for unpacking
    def __iter__(self):
        yield self
        yield self.lastname

def foo():
    return StrOrPair('Bob', 'Jones')

name = foo()
[first, second] = foo()

print(name) # Bob
print(first) # Bob
print(second) # Jones

# broken iteration over chars:
for c in name:
    print(c) # expect 'B', 'o', 'b' but get 'Bob', 'Jones'

answered Aug 9, 2013 at 10:58

tom

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