Python strings cannot be changed . Not true

[tulliog]

This page
https://docs.python.org/3/tutorial/introduction.html

states: "Python strings cannot be changed — they are immutable".

As it is written, it is a wrong statement. This example proves it:

>>> myString = 'Python3'
>>> myString 
'Python3'
>>> myString = 'Perl'
>>> myString 
'Perl'
>>> 

Maybe what the documentation intended to say is that we cannot change parts of strings using indexes.

[AA-Turner]

The string cannot be changed. What can be changed is what the variable name points to. In this instance you have created two different strings.

A

[StanFromIreland]

In your example, you are not changing the string, you are creating a new string. Your conclusion is correct.

I think that with the link to the glossary there is nothing to do.

[ZeroIntensity]

I beg to differ:

import ctypes
import sys

a = "hello world"
b = "gotcha"
ptr_a = (ctypes.c_ubyte * sys.getsizeof(a)).from_address(id(a))
ptr_b = (ctypes.c_ubyte * sys.getsizeof(b)).from_address(id(b))
ctypes.memmove(ptr_a, ptr_b, sys.getsizeof(b))
print("hello world")  # gotcha

[tulliog]

I beg to differ:

import ctypes
import sys

a = "hello world"
b = "gotcha"
ptr_a = (ctypes.c_ubyte * sys.getsizeof(a)).from_address(id(a))
ptr_b = (ctypes.c_ubyte * sys.getsizeof(b)).from_address(id(b))
ctypes.memmove(ptr_a, ptr_b, sys.getsizeof(b))
print("hello world") # gotcha

I am new to Python, i do not understand if your example is disproving my statement, or AA-Turner's statement.

[AA-Turner]

Peter is proving that just because you can do something it doesn't mean you should!

You can safely ignore the example, but it shows how you can directly manipulate the memory that represents a Python str object. This uses the ctypes module, which allows you to make calls to C functions within Python. C is the language that Python is written in. This is entirely unsupported behaviour and we do not condone doing anything like this!

I suggest that you seek advice elsewhere for learning Python, for example StackOverflow, the Discourse forum, or third party tutorials. This issue tracker is not the best place to learn. I wish you the best!

A

[tulliog]

I suggest that you seek advice elsewhere for learning Python, for example StackOverflow, the Discourse forum, or third party tutorials. This issue tracker is not the best place to learn. I wish you the best!

ok thanks. As you can see from my initial post, i am learning Python from
https://docs.python.org/3/tutorial/introduction.html .

I still think that something is not ok with the wording in the tutorial , anyway i will keep using it

[terryjreedy]

The joke in Peter(ZeroIntensity)'s post is that the CPython ctypes module lets one access the C memory blocks wrapped as Python objects and manipulate them in all sorts of ways that violate the Python doc. The later explains what you can do with normal Python code, with it understood that ctypes and any similar modules are not 'normal'.

I learned Python 28 years ago by starting with the tutorial, so it can be done.

[StanFromIreland]

On linux, you get a nice error message if you run it!

>>> import ctypes
... import sys
... 
... a = "hello world"
... b = "gotcha"
... ptr_a = (ctypes.c_ubyte * sys.getsizeof(a)).from_address(id(a))
... ptr_b = (ctypes.c_ubyte * sys.getsizeof(b)).from_address(id(b))
... ctypes.memmove(ptr_a, ptr_b, sys.getsizeof(b))
... print("hello world")  # gotcha
... 
Fatal Python error: unicode_dealloc: We've reached an unreachable state. Anything is possible.
The limits were in our heads all along. Follow your dreams.
https://xkcd.com/2200
Python runtime state: initialized

Current thread 0x00007f30cb7c0780 [python3.14] (most recent call first):
  File "<python-input-1>", line 4 in <module>
  File "/usr/local/lib/python3.14/_pyrepl/console.py", line 181 in runcode
  File "/usr/local/lib/python3.14/_pyrepl/console.py", line 226 in runsource
  File "/usr/local/lib/python3.14/code.py", line 324 in push
  File "/usr/local/lib/python3.14/_pyrepl/simple_interact.py", line 146 in run_multiline_interactive_console
  File "/usr/local/lib/python3.14/_pyrepl/main.py", line 59 in interactive_console
  File "/usr/local/lib/python3.14/_pyrepl/__main__.py", line 10 in <module>
  File "/usr/local/lib/python3.14/runpy.py", line 88 in _run_code
  File "/usr/local/lib/python3.14/runpy.py", line 198 in _run_module_as_main
Aborted (core dumped)

[ethanfurman]

Using a module to poke directly at the computer's memory is not the same as using Python's operators.