How is this "operation" called in Python

Question

I'm trying to understand how this bit works:

Var_1, Var_2, Result =  some_function()

the script:

def some_function():
    return True, False, {"Some": "Dictionary"}

def main():
    Var_1, Var_2, Result =  some_function()
    if not Var_1:
        do something
    else:
        do something_else(Var_2, Result)

if __name__ == '__main__':
    main()

For me the difficult to grasp is the bit of doing inception and provide(return) values which will be used in the main function and in the same trigger the some_function() from within the main() function.

Since I'm new to advanced concepts in python, I found it really interesting. How this "operation" is called so I can read a bit more about how it works. i.e. returning some values in line order separated by , and interpreting them based on the position in line(for the lack of better description).

follow this https://stackoverflow.com/questions/39345995/how-does-python-return-multiple-values-from-a-function — Achyuta nanda sahoo, Jul 11 '17 at 08:45

score 5 · Accepted Answer · answered Jul 11 '17 at 08:37

5

It's returning a tuple. A tuple in Python is similar to a list, but it's immutable: you can't add, remove or replace items.

Often, tuples are constructed with the syntax (a, b, c), but the parentheses are optional in many cases, so a, b, c is also valid.

On the receiving end, tuple unpacking is used to get the individual elements of the tuple, and assign them to separate variables.

answered Jul 11 '17 at 08:37

Thomas

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One nice usage: you can use the power of tuple unpacking to switch values: `a, b = b, a`. – Matthias Jul 11 '17 at 08:44

Jonas Adler · Answer 2 · 2017-07-11T08:48:26.473

3

What is happening here is in fact not that several values are returned. Instead, a single tuple is returned, and this is then unpacked using something called tuple unpacking.

The code is equivalent to

tmp_tuple = some_function()  # return tuple
Var_1, Var_2, Result = tmp_tuple  # unpack tuple

edited Jul 11 '17 at 08:48

answered Jul 11 '17 at 08:34

Jonas Adler

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maestromusica · Answer 3 · 2017-07-11T08:48:24.807

some_function() returns a tuple (True, False, {"Some": "Dictionary"}).

Tuples are very useful for grouping related data, for example something like ('John Smith', 1960, 'England', 'London', 'Newham') might be a better way to store information about a person then creating 5 separate variables.

When Var_1, Var_2, Result = tmp_tuple is called this tuple is unpacked:

 (Var_1, Var_2, Result) = (True, False, {"Some": "Dictionary"})

And hence:

Var_1 = True
Var_2 = False
Result = {"Some": "Dictionary"}

score 0 · Answer 4 · answered Jul 11 '17 at 08:40

The docs say:

Except when part of a list or set display, an expression list containing at least one comma yields a tuple

This means return x,y will return a single object - a tuple and the rest is just unpacking it to the separate values.

So i would say those are two operation: tuple creation in return statement and tuple unpacking in main.

How is this "operation" called in Python

4 Answers4