How can I pass a tuple with a single string as an argument (e.g. to mulitprocessing.Process)?
arguments, multiprocessing, python, string
Solution
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".
Problem
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 is the code: ``` import multiprocessing def write(s): print s write('hello') p = multiprocessing.Process(target=write, args=('hello')) p.start() ``` I get this output: ``` hello Process Process-1: Traceback (most recent call last): >>> File "/usr/local/lib/python2.5/site-packages/multiprocessing/process.py", line 237, in _bootstrap self.run() File "/usr/local/lib/python2.5/site-packages/multiprocessing/process.py", line 93, in run self._target(*self._args, **self._kwargs) TypeError: write() takes exactly 1 argument (5 given) >>> ``` What am I doing wrong? How am I supposed to pass a string?