How can I copy a Python string?

How can I copy a Python string?

You dont need to copy a Python string. They are immutable, and the copy module always returns the original in such cases, as do str(), the whole string slice, and concatenating with an empty string.

Moreover, your hello string is interned (certain strings are). Python deliberately tries to keep just the one copy, as that makes dictionary lookups faster.

One way you could work around this is to actually create a new string, then slice that string back to the original content:

>>> a = hello
>>> b = (a + .)[:-1]
>>> id(a), id(b)
(4435312528, 4435312432)

But all you are doing now is waste memory. It is not as if you can mutate these string objects in any way, after all.

If all you wanted to know is how much memory a Python object requires, use sys.getsizeof(); it gives you the memory footprint of any Python object.

For containers this does not include the contents; youd have to recurse into each container to calculate a total memory size:

>>> import sys
>>> a = hello
>>> sys.getsizeof(a)
>>> b = {foo: bar}
>>> sys.getsizeof(b)
>>> sys.getsizeof(b) + sum(sys.getsizeof(k) + sys.getsizeof(v) for k, v in b.items())

You can then choose to use id() tracking to take an actual memory footprint or to estimate a maximum footprint if objects were not cached and reused.

You can copy a string in python via string formatting :

>>> a = foo  
>>> b = %s % a  
>>> id(a), id(b)  
(140595444686784, 140595444726400)  

How can I copy a Python string?

Im just starting some string manipulations and found this question. I was probably trying to do something like the OP, usual me. The previous answers did not clear up my confusion, but after thinking a little about it I finally got it.

As long as a, b, c, d, and e have the same value, they reference to the same place. Memory is saved. As soon as the variable start to have different values, they get start to have different references. My learning experience came from this code:

import copy
a = hello
b = str(a)
c = a[:]
d = a + 
e = copy.copy(a)

print map( id, [ a,b,c,d,e ] )

print a, b, c, d, e

e = a + something
a = goodbye
print map( id, [ a,b,c,d,e ] )
print a, b, c, d, e

The printed output is:

[4538504992, 4538504992, 4538504992, 4538504992, 4538504992]

hello hello hello hello hello

[6113502048, 4538504992, 4538504992, 4538504992, 5570935808]

goodbye hello hello hello hello something

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