Converting Exception to a string in Python 3

Question

does anyone have an idea, why this Python 3.2 code

try:    
    raise Exception('X')
except Exception as e:
    print("Error {0}".format(str(e)))

works without problem (apart of unicode encoding in windows shell :/),
but this

try:    
    raise Exception('X')
except Exception as e:
    print("Error {0}".format(str(e, encoding = 'utf-8')))

throws TypeError: coercing to str: need bytes, bytearray or buffer-like object, Exception found ?

How to convert an Error to a string with custom encoding?

Edit

It does not works either, if there is u2019 in message:

try:    
    raise Exception(msg)
except Exception as e:
    b = bytes(str(e), encoding = 'utf-8')
    print("Error {0}".format(str(b, encoding = 'utf-8')))

But why cannot str() convert an exception internally to bytes?

Asked By: ts.

||

Source

Answer 1

In Python3, string does not have such attribute as encoding. It’s always unicode internally. For encoded strings, there are byte arrays:

s = "Error {0}".format(str(e)) # string
utf8str = s.encode("utf-8") # byte array, representing utf8-encoded text

Answered By: hamstergene

Answer 2

Try this, it should work.

try:    
    raise Exception('X')
except Exception as e:
    print("Error {0}".format(str(e.args[0])).encode("utf-8"))

Considering you have only a message in your internal tuple.

Answered By: Sebastiano Merlino

Answer 3

In Python 3.x, str(e) should be able to convert any Exception to a string, even if it contains Unicode characters.

So unless your exception actually returns an UTF-8 encoded byte array in its custom __str__() method, str(e, 'utf-8') will not work as expected (it would try to interpret a 16bit Unicode character string in RAM as an UTF-8 encoded byte array …)

My guess is that your problem isn’t str() but the print() (i.e. the step which converts the Python Unicode string into something that gets dumped on your console). See this answer for solutions: Python, Unicode, and the Windows console

Answered By: Aaron Digulla

Answer 4

In Python 3, you are already in “unicode space” and don’t need encoding. Depending on what you want to achieve, you should the conversion do immediately before doing stuff.

E.g. you can convert all this to bytes(), but rather in the direction

bytes("Error {0}".format(str(e)), encoding='utf-8')

.

Answered By: glglgl

Answer 5

There is a version-agnostic conversion here:

# from the `six` library
import sys
PY2 = sys.version_info[0] == 2
if PY2:
    text_type = unicode
    binary_type = str
else:
    text_type = str
    binary_type = bytes

def exc2str(e):
    if e.args and isinstance(e.args[0], binary_type):
        return e.args[0].decode('utf-8')
    return text_type(e)

and tests for it:

def test_exc2str():
    a = u"u0856"
    try:
        raise ValueError(a)
    except ValueError as e:
        assert exc2str(e) == a
        assert isinstance(exc2str(e), text_type)
    try:
        raise ValueError(a.encode('utf-8'))
    except ValueError as e:
        assert exc2str(e) == a
        assert isinstance(exc2str(e), text_type)
    try:
        raise ValueError()
    except ValueError as e:
        assert exc2str(e) == ''
        assert isinstance(exc2str(e), text_type)

Answered By: tsionyx

Answer 6

You can use the traceback module.

If you want to print the error:

import traceback
traceback.print_exc()

If you want to convert to string:

import traceback
print("Error {0}".format(traceback.format_exc()))

Answered By: XLBilly

Converting Exception to a string in Python 3

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