Executing code in parallel with python

Question

I am trying to use multithreading in python. I wrote the following code to start. It is supposed to compute, in parallel, the squares of numbers contained in a list and to return the result in a list named 'result'. I wrote this in order to parallelize a script that contains a for loop.

However, I get a TypeError telling me that 'int object is not callable'. I am guessing this is because of this line of code: thr.append(threading.Thread(target=square(k))): In the examples I read, target was a function. But in my example, I will need to call the same function with different arguments. How can I do that?

>>> def square(c):
...     return c^2
...     result.append(c^2)
... 



>>> def sqr():
...     thr = []
...     for k in l:
...         thr.append(threading.Thread(target=square(k)))
...     for t in thr:
...         t.start()
...     for i in thr:
...         t.join()

Note that most of the time parallel computations with Python (in its standard CPython implementation) doesn't really work because of the GIL — hivert
– hivert, Commented Mar 10, 2014 at 13:35

gravetii · Accepted Answer · 2014-04-16 10:40:07Z

5

Try this:

thr.append(threading.Thread(target=square, args=(k,)))

instead of thr.append(threading.Thread(target=square(k)))

You get that error because you end up calling the function in your code. When the function is called, square(k) returns an int which is not callable.

Refer to the documentation.

Also, as unutbu has pointed out in the comments to the question, you are doing an XOR and not computing the square. Squares are computed this way: x**2 and not x^2.

Also, you are returning the result before adding it to the list, so you might want to reverse the order of the two lines in your function definition if you want to add the square of the number to the list, result.

edited Apr 16, 2014 at 10:40

answered Mar 10, 2014 at 13:32

gravetii

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