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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?
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Copying one string to another - strcpystrcpy can be used to copy one string to another. Remember that C strings are character arrays. You must pass character array, or pointer to character array to this function where string will be copied.
Copy List Python: copy() Method. The Python copy() method creates a copy of an existing list. The copy() method is added to the end of a list object and so it does not accept any parameters. copy() returns a new list.
In Python, we utilize the asterisk operator to repeat a string. This operator is indicated by a “*” sign. This operator iterates the string n (number) of times.
Since string is immutable, we can get a new copy of the string by adding an empty string to the original string. Also, we can slice the whole string or use str () function to get a copy of a string.
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.
Using the inbuilt function strcpy () from string.h header file to copy one string to the other. strcpy () accepts a pointer to the destination array and source array as a parameter and after copying it returns a pointer to the destination 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:
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:
>>> 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; you'd have to recurse into each container to calculate a total memory size:
>>> import sys >>> a = 'hello' >>> sys.getsizeof(a) 42 >>> b = {'foo': 'bar'} >>> sys.getsizeof(b) 280 >>> 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.
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You can copy a string in python via string formatting :
>>> a = 'foo' >>> b = '%s' % a >>> id(a), id(b) (140595444686784, 140595444726400) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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