CODEWITHSUNDEEP
pythonstringoperators
Tasdik Rahman
Tasdik Rahman

Reputation: 2340

In python, why is s*3 faster than s+s+s?

I was going through the google's python intro and came across the statement that s * 3 is faster than doing s + s + s where s is of type string.

Any reason for that to happen?

I googled and found which is faster s+='a' or s=s+'a' in python. But that didn't help

Upvotes: 3

Views: 435

Answers (2)

Andy Wong
Andy Wong

Reputation: 351

You can also test it yourself here:

import timeit

print(timeit.timeit("string=''; string='s'+'s'+'s'", number=10000))
print(timeit.timeit("string2=''; string2='s'*3", number=10000))

My guess is that s*3 treats it as one operation vs. two with s+s+s.

Upvotes: 3

jonrsharpe
jonrsharpe

Reputation: 122157

Because s * 3 is one operation, whereas s + s + s is two operations; it's really (s + s) + s, creating an additional string object that then gets discarded.

You can see the difference by using dis to look at the bytecode each generates:

s + s + s:

  3           0 LOAD_FAST                0 (s)
              3 LOAD_FAST                0 (s)
              6 BINARY_ADD          
              7 LOAD_FAST                0 (s)
             10 BINARY_ADD          
             11 RETURN_VALUE

s * 3:

  3           0 LOAD_FAST                0 (s)
              3 LOAD_CONST               1 (3)
              6 BINARY_MULTIPLY     
              7 RETURN_VALUE

Upvotes: 18

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