CODEWITHSUNDEEP
pythonexceptionout-of-memory
Imanol Luengo
Imanol Luengo

Reputation: 15909

MemoryError's message as str is empty in Python

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?

Upvotes: 6

Views: 2168

Answers (3)

Juergen
Juergen

Reputation: 12728

From the Python documentation (Version 2.7, I guess also applies to Python 3.x):

The base class for all built-in exceptions. It is not meant to be directly inherited by user-defined classes (for that, use Exception). If str() or unicode() is called on an instance of this class, the representation of the argument(s) to the instance are returned, or the empty string when there were no arguments.

It seems, that MemoryError gets no arguments, and thus according to this documentation does give an empty string back.

The exception can of course still be catched, because it can be catched by its type.

You can get the name of the exception class and print that.

This makes of course also a lot of sense, since look at that:

a = {}
try:
    a['barrel']
except Exception as e:
    print str(e)

Will print just 'barrel' -- what is not so helpful, so to add the class name of the exception is really a good idea:

...
except Exception as e:
    print(e.__class__.__name + ': ' + (str(e)))

Upvotes: 1

Anand S Kumar
Anand S Kumar

Reputation: 90979

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))

Upvotes: 4

Bakuriu
Bakuriu

Reputation: 101989

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)

Upvotes: 5

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