Aren't Python strings immutable? Then why does a + " " + b work?

python string immutability mutability
jason picture jason · Feb 1, 2012 · Viewed 124.9k times · Source

My understanding was that Python strings are immutable.

I tried the following code:

a = "Dog"
b = "eats"
c = "treats"

print a, b, c
# Dog eats treats

print a + " " + b + " " + c
# Dog eats treats

print a
# Dog

a = a + " " + b + " " + c
print a
# Dog eats treats
# !!!

Shouldn't Python have prevented the assignment? I am probably missing something.

Any idea?

Answer

Bort picture Bort · Feb 1, 2012

First a pointed to the string "Dog". Then you changed the variable a to point at a new string "Dog eats treats". You didn't actually mutate the string "Dog". Strings are immutable, variables can point at whatever they want.

Related questions

Remove specific characters from a string in Python

I'm trying to remove specific characters from a string using Python. This is the code I'm using right now. Unfortunately it appears to do nothing to the string. for char in line: if char in " ?.!/;:": line.replace(char,'') How …

Read More
Why are Python strings immutable? Best practices for using them

What are the design reasons of making Python strings immutable? How does it make programming easier? I'm used to mutable strings, like the ones in C. How am I supposed to program without mutable strings? Are there any best practices?

Read More
Why are python strings and tuples are made immutable?

I am not sure why strings and tuples were made to be immutable; what are the advantages and disadvantage of making them immutable?

Read More