Syntactical comma use

Asked Oct 13 '15 at 10:11

Active Oct 13 '15 at 10:19

Viewed 31 times

def swap(s1,s2):
    if len(s1) > len(s2):
        s1, s2 = s2, s1
        return (s1, s2)

str1 = "cheese"
str2 = "spoon"

str3, str4 = swap(str1, str2)

print ("%s, %s : %s, %s" % (str1, str2, str3, str4))

I noticed from Levenshtein Distance code that an easy way to swap over variables is

s1, s2 = s2, s1

but to unpack from the function we use

str3, str4 = ...

To me they look like the same thing, but I know they're not. Can someone clarify the use of the comma in these cases?

edited May 23 '17 at 11:52

Community

asked Oct 13 '15 at 10:11

Mr Mystery Guest

1,378
15
45

1

*"To me they look the same thing, but I know they're not"* - why do you think they're not? In both cases, you're assigning two items to two names. – jonrsharpe Oct 13 '15 at 10:16
1

`s1, s2 = s2, s1` is the same as `s1, s2 = (s2, s1)` (hint: try `a = 1, 2`), so it is always tuple unpacking. The difference is purely syntactical. – dhke Oct 13 '15 at 10:16
See also http://stackoverflow.com/q/16409901/3001761, http://stackoverflow.com/q/8725673/3001761, etc. – jonrsharpe Oct 13 '15 at 10:19
1

@jonrsharpe I was unaware that in Python tuples can often be written with or without the parentheses. Learning, me. – Mr Mystery Guest Oct 13 '15 at 10:41
Ah, I see. Yes, you could also have `return s1, s2` in the function - the comma is the important part of the syntax. – jonrsharpe Oct 13 '15 at 10:42
@jonrsharpe Thanks for the clarity. – Mr Mystery Guest Oct 13 '15 at 10:57

Syntactical comma use

0 Answers0