How to share a string amongst multiple processes using Managers() in Python?

multiprocessing's Managers can hold Values which in turn can hold instances of the type c_char_p from the ctypes module:

>>> import multiprocessing>>> import ctypes>>> v = multiprocessing.Value('c', "Hello, World!")Traceback (most recent call last):  File "<stdin>", line 1, in <module>  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 253, in Value    return Value(typecode_or_type, *args, **kwds)  File "/usr/lib/python2.7/multiprocessing/sharedctypes.py", line 99, in Value    obj = RawValue(typecode_or_type, *args)  File "/usr/lib/python2.7/multiprocessing/sharedctypes.py", line 73, in RawValue    obj.__init__(*args)TypeError: one character string expected>>> cstring = multiprocessing.Value(ctypes.c_char_p, "Hello, World!")>>> cstring<Synchronized wrapper for c_char_p(166841564)>>>> cstring.value'Hello, World!'

For Python 3, use c_wchar_p instead of c_char_p

See also: Post with the original solution that I had a hard time finding.

So a Manager can be used to share a string beneath multiple processes in Python like this:

>>> from multiprocessing import Process, Manager, Value>>> from ctypes import c_char_p>>> >>> def greet(string):>>>     string.value = string.value + ", World!">>> >>> if __name__ == '__main__':>>>     manager = Manager()>>>     string = manager.Value(c_char_p, "Hello")>>>     process = Process(target=greet, args=(string,))>>>     process.start()>>>     process.join()    >>>     print string.value'Hello, World!'

Simply put the string in a dict:

d = manager.dict()d['state'] = 'xyz'

As strings themselves are immutable, sharing one directly would not be as useful.