Python Debugger Functions Do Not Exist

Question

The pdb module should contain a function called set_trace, however, when I run the code import pdb; pdb.set_trace() I get an error message saying module 'pdb' has no attribute 'set_trace'. Why is this error happening, even though my code is correct?

Here the code.py file I am executing to get this error:

print("Hello, World!")
import pdb
pdb.set_trace()
print("Goodbye, World!")

And here is the complete output of my program:

Hello, World!
Hello, World!
Traceback (most recent call last):
  File "code.py", line 3, in 
    import pdb
  File "/usr/lib/python3.6/pdb.py", line 76, in 
    import code
  File "/tmp/code.py", line 4, in 
    pdb.set_trace()

Einhaender · Accepted Answer · 2018-06-23 20:07:43Z

One of the first things that pdb does after you execute it is import a module called code. However, since you've named your file code.py Python ends up executing both files. When your file is executed for the second time, it prints the "Hello, World!" message again. At this point, Python is still processing the first import pdb statement when it encounters the same statement again. In a language like C, this would result in infinite recursion, but Python automatically ignores duplicate imports (documentation). Thus, Python ends up executing the next line of your code, pdb.set_trace(), before the initial import pdb statement finished executing, which is why you see an error message telling you that pdb.set_trace() does not exist.

To fix this, you could just rename your file to something else, but it would be better to add a check so that your code doesn't execute when it is imported by a different file:

if __name__ == "__main__":
    print("Hello, World!")
    import pdb
    pdb.set_trace()
    print("Goodbye, World!")

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