MemoryError's message as str is empty in Python

Question

This is a very silly question, but I'm running some tasks and catching their errors by:

try:
    run_something()
except Exception as e:
    handle_error(str(e))

I want the error message as a String because I'm using a UI and I want to display the error in a window.

The problem can be replicated as:

>>> import numpy as np
>>> np.range(1e10)
MemoryError                               Traceback (most recent call last)
<ipython-input-4-20a59c2069b2> in <module>() 
----> 1 np.arange(1e10)

MemoryError: 

However, if I try to catch the error and print its message (which I was hoping to be something like "MemoryError":

try:
    np.arange(1e10)
except Exception as e:
    print(str(e))
    print("Catched!")

The only output I get is "Catched!". This is so stupid, I was doing some work with UI's and threading, and took me a while to realise that the problem was a memory error with no message at all.

Is the MemoryError the only Exception that is translated to an empty string? Because if it is the case I can check it. If not, how to get its message as a String?

Answer 1

So you probably want to print the name of the exception class:

try:
    np.arange(1e10)
except Exception as e:   #not catch...
    print(str(e.__class__.__name__))
    print("Catched!")

Using str(e) only prints the "message" of the exception, which in your case was empty.

---

Note that you can obtain the arguments passed to the exception constructor via the args attribute:

In [4]: try:
   ...:     raise ValueError(1,2,3)
   ...: except ValueError as e:
   ...:     print('arguments:', e.args)
arguments: (1, 2, 3)

Answer 2

When call str(e) it returns the message of the Exception. Take an example -

NameError: name 'a' is not defined
^          ^
name       message

The part before : is the name of the exception, whereas the part after it is the message (arguments).

In the case of MemoryError , as you can see in your example -

MemoryError:

does not have an error message , only the name of the exception , hence you get the empty string.

I am not sure if there are other Exceptions that do not have an exception, but I believe it would be very rare to find such exceptions. Maybe you can print both the exception's name as well as the message , if you really want to take care of the MemoryError (and maybe other such rare exceptions without messages) , something like -

print(type(e).__name__ , ':', str(e))