How can I copy a Python string

Question

I do this   a    hello    And now I just want an independent copy of a   import copy  b   str a  c   a    d   a      e   copy copy a   map  id    a b c d e       Out 3     4365576160  4365576160  4365576160  4365576160  4365576160    Why do they all have the same memory address and how can I get a copy of a

User · Answer

Copying a string can be done two ways either copy the location a    a  b   a or you can clone which means b wont get affected when a is changed which is done by a    a  b   a

User · Answer

To put it a different way  id    is not what you care about  You want to know if the variable name can be modified without harming the source variable name    gt  gt  gt  a    hello                                                                                                                                                                                                                                                                                           gt  gt  gt  b   a                                                                                                                                                                                                                                                                                                gt  gt  gt  c   a                                                                                                                                                                                                                                                                                                gt  gt  gt  b      world                                                                                                                                                                                                                                                                                         gt  gt  gt  c       bye                                                                                                                                                                                                                                                                                          gt  gt  gt  a                                                                                                                                                                                                                                                                                                    hello                                                                                                                                                                                                                                                                                                   gt  gt  gt  b                                                                                                                                                                                                                                                                                                    hello world                                                                                                                                                                                                                                                                                             gt  gt  gt  c                                                                                                                                                                                                                                                                                                    hello  bye                                                                                                                                                                                                                                                                                               If you re used to C  then these are like pointer variables except you can t de-reference them to modify what they point at  but id   will tell you where they currently point   The problem for python programmers comes when you consider deeper structures like lists or dicts    gt  gt  gt  o   a   10                                                                                                                                                                                                                                                                                           gt  gt  gt  x o                                                                                                                                                                                                                                                                                                  gt  gt  gt  y o copy                                                                                                                                                                                                                                                                                             gt  gt  gt  x  a     20                                                                                                                                                                                                                                                                                          gt  gt  gt  y  a     30                                                                                                                                                                                                                                                                                          gt  gt  gt  o                                                                                                                                                                                                                                                                                                     a   20                                                                                                                                                                                                                                                                                                 gt  gt  gt  x                                                                                                                                                                                                                                                                                                     a   20                                                                                                                                                                                                                                                                                                 gt  gt  gt  y                                                                                                                                                                                                                                                                                                     a   30                                                                                                                                                                                                                                                                                                  Here o and x refer to the same dict o  a   and x  a    and that dict is  mutable  in the sense that you can change the value for key  a   That s why  y  needs to be a copy and y  a   can refer to something else

User · Answer

You don t 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    gt  gt  gt  a    hello   gt  gt  gt  b    a         -1   gt  gt  gt  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  you d have to recurse into each container to calculate a total memory size    gt  gt  gt  import sys  gt  gt  gt  a    hello   gt  gt  gt  sys getsizeof a  42  gt  gt  gt  b     foo    bar    gt  gt  gt  sys getsizeof b  280  gt  gt  gt  sys getsizeof b    sum sys getsizeof k    sys getsizeof v  for k  v in b items    360   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

User · Answer

I m 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

User · Answer

You can copy a string in python via string formatting       gt  gt  gt  a    foo     gt  gt  gt  b     s    a    gt  gt  gt  id a   id b     140595444686784  140595444726400

[python] How can I copy a Python string?

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