String arguments in python multiprocessing

Question

I\'m trying to pass a string argument to a target function in a process. Somehow, the string is interpreted as a list of as many arguments as there are characters.

This

Answer 1

Change args=('hello') to args=('hello',) or even better args=['hello']. Otherwise parentheses don't form a sequence.

Answer 2

You have to pass

p = multiprocessing.Process(target=write, args=('hello',))

Notice the comma! Otherwise it is interpreted as a simple string and not as a 1 element tuple.

Answer 3

This is a common gotcha in Python - if you want to have a tuple with only one element, you need to specify that it's actually a tuple (and not just something with brackets around it) - this is done by adding a comma after the element.

To fix this, just put a comma after the string, inside the brackets:

p = multiprocessing.Process(target=write, args=('hello',))

That way, Python will recognise it as a tuple with a single element, as intended. Currently, Python is interpreting your code as just a string. However, it's failing in this particular way because a string is effectively list of characters. So Python is thinking that you want to pass ('h', 'e', 'l', 'l', 'o'). That's why it's saying "you gave me 5 parameters".