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When try to %timeit in Jupyter Notebook got error; Without it working fine.

UnboundLocalError: local variable 'a' referenced before assignment

import torch
a = torch.rand(10)
b = torch.rand(10)

%timeit a = torch.where(b > 0.5, torch.tensor(0.), a)

What is happening here?

Red
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Dishin H Goyani
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  • Does this answer your question? [ipython %timeit "local variable 'a' referenced before assignment"](https://stackoverflow.com/questions/48269712/ipython-timeit-local-variable-a-referenced-before-assignment) – Shiva May 25 '20 at 14:54

1 Answers1

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At first, I thought that's because %timeit only evaluates the time run by functions. But thanks to @Shiva who told me it can calculate the execution time of other things. And I checked the documentation here, and I found out this is true.

So, according to this answer, %timeit has a problem with re-assignment as the re-assignment to a causes the function to have an a local variable, hiding the global. In other words, you can use any other variable other that a to assign it to torch.where:

#this works
%timeit c = torch.where(b > 0.5, torch.tensor(0.), a) #c instead of a

# this works
%timeit torch.where(b > 0.5, torch.tensor(0.), a)

# this doesn't work
%timeit a = torch.where(b > 0.5, torch.tensor(0.), a)
Anwarvic
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    The argument to `%timeit` need not be a function, it can be any expression or statement(including a function statement) – Shiva May 25 '20 at 14:51
  • yeah... you're right. I didn't know that till now. Gonna edit my answer. Thanks – Anwarvic May 25 '20 at 14:53