Assign multiple variables at once with dynamic variable names [duplicate]

Question

I'm aware I can assign multiple variables to multiple values at once with:

(foo, bar, baz) = 1, 2, 3

And have foo = 1, bar = 2, and so on.

But how could I make the names of the variables more dynamic? Ie,

somefunction(data,tupleofnames):
    (return that each name mapped to a single datum)

somefunction((1,2,3),(foo,bar,baz))     

And have the same?

Horseback

What is this act of assigning variables like this (foo, bar, baz = 1,2,3) called? (as opposed to assigning foo = 1, bar = 2, baz = 3). Thanks! – Ferine

Hi @sindhus! It's called 'destructuring assignment'. Python's had it for a while, and it was recently added to JavaScript. – Horseback

Answer 1

How about this?

def somefunction(data, tupleofnames):
    length = len(tupleofnames)
    for i in range(0, length):
        globals()[tupleofnames[i]] = data[i]

Here I assume both data and tupleofnames are lists where tupleofnames is a list of strings. But as Thomas mentioned this is not a good practice. It can easily corrupt your app.

Require

After some deliberation: while I understand assigning what seems like arbitrary variable names can be a bad idea, I like this answer because it shows it's possible (and my interest is mainly academic). Thanks for your answer! – Horseback

Answer 2

There are ways to do it, but they're not nice ways, and it's considered bad practice in Python. New variables shouldn't be created by magic. If you want to have a collection of things, use a list, dictionary or set, as appropriate.

For example, you could return a dictionary: {"foo":1, "bar":2, "baz":3}

Brunt

Answer 3

If dictionaries are not what you want, then possibly namedtuple's are the way to go: they allow for efficient creation of several instances of data grouped together, with named attributes.

http://docs.python.org/library/collections.html#collections.namedtuple

from collections import namedtuple


mytype = namedtuple("mytype", "foo bar baz")

a = mytype(1,2,3)
a.foo
1
a.bar
2
a.baz
 3

Ropy

Answer 4

You can do it like this:

    (foo, bar, baz) = (1, 2, 3)

Crocoite

and then even (foo, bar, baz) = [None] * 3 – Hamill

This appears to be functionally identically to the first line of code in the question, and definitely doesn't involve dynamic variable names - did you even read any part of the question body, or just the title? Or am I missing something? – Foreglimpse

Answer 5

Check out the help docs for zip & map. e.g. for zip:-

>>>  zip( (1,2,3) , ('foo','bar','baz') )
[(1, 'foo'), (2, 'bar'), (3, 'baz')] 

map requires a function to map sequences together. But, you can use None instead of a function to return the same results as zip does, above.

>>> map( None, (1,2,3) , ('foo','bar','baz') )                                                                                       
[(1, 'foo'), (2, 'bar'), (3, 'baz')]

Annexation

what is the point of using map here? this is exactly what zip is intended for! – Marco

Answer 6

(foo, bar, baz) = [None] * 3    
a,b,c = [0]*3    
a,b,c = ["nihao"]*3

Watersoak

Answer 7

I understand the answers above are already all they need, but I have a nice cool programming trick that could also help you when you want to assign a particular tuple to variables.

tuple T

T = (A,B,C)

the variables

var1, var2, var3 = T

Circumfluous