Python try except как вывести текст ошибки

One has pretty much control on which information from the traceback to be displayed/logged when catching exceptions.

The code

with open("not_existing_file.txt", 'r') as text:
    pass

would produce the following traceback:

Traceback (most recent call last):
  File "exception_checks.py", line 19, in <module>
    with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'

Print/Log the full traceback

As others already mentioned, you can catch the whole traceback by using the traceback module:

import traceback
try:
    with open("not_existing_file.txt", 'r') as text:
        pass
except Exception as exception:
    traceback.print_exc()

This will produce the following output:

Traceback (most recent call last):
  File "exception_checks.py", line 19, in <module>
    with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'

You can achieve the same by using logging:

try:
    with open("not_existing_file.txt", 'r') as text:
        pass
except Exception as exception:
    logger.error(exception, exc_info=True)

Output:

__main__: 2020-05-27 12:10:47-ERROR- [Errno 2] No such file or directory: 'not_existing_file.txt'
Traceback (most recent call last):
  File "exception_checks.py", line 27, in <module>
    with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'

Print/log error name/message only

You might not be interested in the whole traceback, but only in the most important information, such as Exception name and Exception message, use:

try:
    with open("not_existing_file.txt", 'r') as text:
        pass
except Exception as exception:
    print("Exception: {}".format(type(exception).__name__))
    print("Exception message: {}".format(exception))

Output:

Exception: FileNotFoundError
Exception message: [Errno 2] No such file or directory: 'not_existing_file.txt'

One has pretty much control on which information from the traceback to be displayed/logged when catching exceptions.

The code

with open("not_existing_file.txt", 'r') as text:
    pass

would produce the following traceback:

Traceback (most recent call last):
  File "exception_checks.py", line 19, in <module>
    with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'

Print/Log the full traceback

As others already mentioned, you can catch the whole traceback by using the traceback module:

import traceback
try:
    with open("not_existing_file.txt", 'r') as text:
        pass
except Exception as exception:
    traceback.print_exc()

This will produce the following output:

Traceback (most recent call last):
  File "exception_checks.py", line 19, in <module>
    with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'

You can achieve the same by using logging:

try:
    with open("not_existing_file.txt", 'r') as text:
        pass
except Exception as exception:
    logger.error(exception, exc_info=True)

Output:

__main__: 2020-05-27 12:10:47-ERROR- [Errno 2] No such file or directory: 'not_existing_file.txt'
Traceback (most recent call last):
  File "exception_checks.py", line 27, in <module>
    with open("not_existing_file.txt", 'r') as text:
FileNotFoundError: [Errno 2] No such file or directory: 'not_existing_file.txt'

Print/log error name/message only

You might not be interested in the whole traceback, but only in the most important information, such as Exception name and Exception message, use:

try:
    with open("not_existing_file.txt", 'r') as text:
        pass
except Exception as exception:
    print("Exception: {}".format(type(exception).__name__))
    print("Exception message: {}".format(exception))

Output:

Exception: FileNotFoundError
Exception message: [Errno 2] No such file or directory: 'not_existing_file.txt'

Введение

Если в коде есть ошибка, которую видит интерпретатор поднимается исключение, создается так называемый
Exception Object, выполнение останавливается, в терминале
показывается Traceback.

Исключение, которое предусмотрено в коде называется обработанным (Handled)

Блок try except имеет следующий синтаксис

try:
pass
except Exception:
pass
else:
pass
finally:
pass

В этой статье я создал файл

try_except.py

куда копирую код из примеров.

Пример

Попробуем открыть несуществующий файл и воспользоваться базовым Exception

try:
f = open(‘missing.txt’)
except Exception:
print(‘ERR: File not found’)

python try_except.py

ERR: No missing.txt file found

Ошибка поймана, видно наше сообщение а не Traceback

Проверим, что когда файл существует всё хорошо

try:
f = open(‘existing.txt’)
except Exception:
print(‘ERR: File not found’)

python try_except.py

Пустота означает успех

Два исключения

Если ошибок больше одной нужны дополнительные исключения. Попробуем открыть существующий файл, и после этого
добавить ошибку.

try:
f = open(‘existing.txt’)
x = bad_value
except Exception:
print(‘ERR: File not found’)

python try_except.py

ERR: File not found

Файл открылся, но так как в следующей строке ошибка — в терминале появилось вводящее в заблуждение сообщение.
Проблема не в том, что «File not found» а в том, что bad_value нигде не определёно.

Избежать сбивающих с толку сообщений можно указав тип ожидаемой ошибки. В данном примере это FileNotFoundError

try:
# expected exception
f = open(‘existing.txt’)
# unexpected exception should result in Traceback
x = bad_value
except FileNotFoundError:
print(‘ERR: File not found’)

python try_except.py

Traceback (most recent call last):
File «/home/andrei/python/try_except2.py», line 5, in <module>
x = bad_value
NameError: name ‘bad_value’ is not defined

Вторая ошибка не поймана поэтому показан Traceback

Поймать обе ошибки можно добавив второй Exception

try:
# expected exception should be caught by FileNotFoundError
f = open(‘missing.txt’)
# unexpected exception should be caught by Exception
x = bad_value
except FileNotFoundError:
print(‘ERR: File not found’)
except Exception:
print(‘ERR: Something unexpected went wrong’)

python try_except.py

ERR: File not found

ERR: Something unexpected went wrong

Печать текста ошибки

Вместо своего текста можно выводить текст ошибки. Попробуем с существующим файлом — должна быть одна пойманная ошибка.

try:
# expected exception should be caught by FileNotFoundError
f = open(‘existing.txt’)
# unexpected exception should be caught by Exception
x = bad_value
except FileNotFoundError as e:
print(e)
except Exception as e:
print(e)

python try_except.py

name ‘bad_value’ is not defined

Теперь попытаемся открыть несуществующий файл — должно быть две пойманные ошибки.

try:
# expected exception should be caught by FileNotFoundError
f = open(‘missing.txt’)
# unexpected exception should be caught by Exception
x = bad_value
except FileNotFoundError as e:
print(e)
except Exception as e:
print(e)

python try_except.py

name ‘bad_value’ is not defined

[Errno 2] No such file or directory: ‘missing.txt’

else

try:
f = open(‘existing.txt’)
except FileNotFoundError as e:
print(e)
except Exception as e:
print(e)
else:
print(f.read())
f.close()

python try_except.py

www.heihei.ru

Если попробовать открыть несуществующий файл

missing.txt

то исключение обрабатывается, а код из блока else не выполняется.

[Errno 2] No such file or directory: ‘missing.txt’

finally

Блок finally будет выполнен независимо от того, поймано исключение или нет

try:
f = open(‘existing.txt’)
except FileNotFoundError as e:
print(e)
except Exception as e:
print(e)
else:
print(f.read())
f.close()
finally:
print(«Finally!»)

www.heihei.ru

Finally!

А если попытаться открыть несуществующий

missing.txt

[Errno 2] No such file or directory: ‘missing.txt’
Finally!

Когда нужно применять finally:

import os

def make_at(path, dir_name):
original_path = os.getcwd()
os.chdir(path)
os.mkdir(dir_name)
os.chdir(original_path)

def make_at(path, dir_name):
original_path = os.getcwd()
os.chdir(path)
try:
os.mkdir(dir_name)
finally:
os.chdir(original_path)

Не лишнима будет добавить обработку и вывод исключения

import os
import sys

def make_at(path, dir_name):
original_path = os.getcwd()
os.chdir(path)
try:
os.mkdir(dir_name)

except OSError as e:
print(e, file=sys.stderr)
raise
finally:
os.chdir(original_path)

По умолчанию print() выводит в sys.stdout, но в случае ислючений логичнее выводить в sys.stderr

raise

Можно вызывать исключения вручную в любом месте кода с помощью
raise.

try:
f = open(‘outdated.txt’)
if f.name == ‘outdated.txt’:
raise Exception
except FileNotFoundError as e:
print(e)
except Exception as e:
print(‘File is outdated!’)
else:
print(f.read())
f.close()
finally:
print(«Finally!»)

python try_except.py

File is outdated!
Finally!

Пример 2

Рассмотрим функцию, которая принимает числа прописью и возвращает цифрами

DIGIT_MAP = {
‘zero’: ‘0’,
‘one’: ‘1’,
‘two’: ‘2’,
‘three’: ‘3’,
‘four’: ‘4’,
‘five’: ‘5’,
‘six’: ‘6’,
‘seven’: ‘7’,
‘eight’: ‘8’,
‘nine’: ‘9’,
}

def convert(s):
number = »
for token in s:
number += DIGIT_MAP[token]
x = int(number)
return x

python

>>> from exc1 import convert
>>> convert(«one three three seven».split())
1337

Теперь передадим аргумент, который не предусмотрен в словаре

>>> convert(«something unseen«.split())
Traceback (most recent call last):
File «<stdin>», line 1, in <module>
File «/home/andrei/python/exc1.py», line 17, in convert
number &plu= DIGIT_MAP[token]
KeyError: ‘something’

KeyError — это тип Exception объекта. Полный список можно изучить в конце статьи.

Исключение прошло следующий путь:

REPL → convert() → DIGIT_MAP(«something») → KeyError

Обработать это исключение можно внеся изменения в функцию convert

convert(s):
try:
number = »
for token in s:
number += DIGIT_MAP[token]
x = int(number)
print(«Conversion succeeded! x = «, x)
except KeyError:
print(«Conversion failed!»)
x = —1
return x

>>> from exc1 import convert
>>> convert(«one nine six one».split())
Conversion succeeded! x = 1961
1961
>>> convert(«something unseen».split())
Conversion failed!
-1

Эта обработка не спасает если передать int вместо итерируемого объекта

>>> convert(2022)
Traceback (most recent call last):
File «<stdin>», line 1, in <module>
File «/home/andrei/python/exc1.py», line 17, in convert
for token in s:
TypeError: ‘int’ object is not iterable

Нужно добавить обработку TypeError

…
except KeyError:
print(«Conversion failed!»)
x = —1
except TypeError:
print(«Conversion failed!»)
x = —1
return x

>>> from exc1 import convert
>>> convert(«2022».split())
Conversion failed!
-1

def convert(s):
«»»Convert a string to an integer.»»»
x = —1
try:
number = »
for token in s:
number += DIGIT_MAP[token]
x = int(number)
except (KeyError, TypeError):
pass
return x

>>> from exc4 import convert
>>> convert(«one nine six one».split())
1961
>>> convert(«bad nine six one».split())
-1
>>> convert(2022)
-1

Ошибки обрабатываются, но без принтов, процесс не очень информативен.

Грамотно показать текст сообщений об ошибках можно импортировав sys и изменив функцию

import sys

DIGIT_MAP = {
‘zero’: ‘0’,
‘one’: ‘1’,
‘two’: ‘2’,
‘three’: ‘3’,
‘four’: ‘4’,
‘five’: ‘5’,
‘six’: ‘6’,
‘seven’: ‘7’,
‘eight’: ‘8’,
‘nine’: ‘9’,
}

def convert(s):
«»»Convert a string to an integer.»»»
try:
number = »
for token in s:
number += DIGIT_MAP[token]
return(int(number))
except (KeyError, TypeError) as e:
print(f«Conversion error: {e!r}», file=sys.stderr)
return —1

>>> from exc1 import convert
>>> convert(2022)
Conversion error: TypeError(«‘int’ object is not iterable»)
-1
>>> convert(«one nine six one».split())
1961
>>> convert(«bad nine six one».split())
Conversion error: KeyError(‘bad’)

raise вместо кода ошибки

def string_log(s):
v = convert(s)
return log(v)

>>> from exc1 import string_log
>>> string_log(«one two eight».split())
4.852030263919617
>>> string_log(«bad one two».split())
Conversion error: KeyError(‘bad’)
Traceback (most recent call last):
File «<stdin>», line 1, in <module>
File «/home/andrei/exc1.py», line 32, in string_log
return log(v)
ValueError: math domain error

convert() вернул -1 а string_log попробовал его обработать и не смог.

Можно заменить return -1 на raise. Это считается более правильным подходом в Python

def convert(s):
«»»Convert a string to an integer.»»»
try:
number = »
for token in s:
number += DIGIT_MAP[token]
return(int(number))
except (KeyError, TypeError) as e:
print(f«Conversion error: {e!r}», file=sys.stderr)
raise

>>> from exc7 import string_log
>>> string_log(«one zero».split())
2.302585092994046
>>> string_log(«bad one two».split())
Conversion error: KeyError(‘bad’)
Traceback (most recent call last):
File «<stdin>», line 1, in <module>
File «/home/andrei/exc7.py», line 31, in string_log
v = convert(s)
File «/home/andrei/exc7.py», line 23, in convert
number += DIGIT_MAP[token]
KeyError: ‘bad’

Пример 3

Рассмотрим алгоритм по поиску квадратного корня

def sqrt(x):
«»»Compute square roots using the method
of Heron of Alexandria.

Args:
x: The number for which the square root
is to be computed.

Returns:
The square root of x.
«»»

guess = x
i = 0
while guess * guess != x and i < 20:
guess = (guess + x / guess) / 2.0
i += 1
return guess

def main():
print(sqrt(9))
print(sqrt(2))

if __name__ == ‘__main__’:
main()

python sqrt_ex.py

3.0
1.414213562373095

При попытке вычислить корень от -1 получим ошибку

def main():
print(sqrt(9))
print(sqrt(2))
print(sqrt(-1))

python sqrt_ex.py

3.0
1.414213562373095
Traceback (most recent call last):
File «/home/andrei/sqrt_ex.py», line 26, in <module>
main()
File «/home/andrei/sqrt_ex.py», line 23, in main
print(sqrt(-1))
File «/home/andrei/sqrt_ex.py», line 16, in sqrt
guess = (guess + x / guess) / 2.0
ZeroDivisionError: float division by zero

В строке

guess = (guess + x / guess) / 2.0

Происходит деление на ноль

Обработать можно следующим образом:

def main():
try:
print(sqrt(9))
print(sqrt(2))
print(sqrt(-1))
except ZeroDivisionError:
print(«Cannot compute square root «
«of a negative number.»)

print(«Program execution continues «
«normally here.»)

Обратите внимание на то, что в try помещены все вызовы функции

python sqrt_ex.py

3.0
1.414213562373095
Cannot compute square root of a negative number.
Program execution continues normally here.

Если пытаться делить на ноль несколько раз — поднимется одно исключение и всё что находится в блоке
try после выполняться не будет

def main():
try:
print(sqrt(9))
print(sqrt(-1))
print(sqrt(2))
print(sqrt(-1))

python sqrt_ex.py

3.0
Cannot compute square root of a negative number.
Program execution continues normally here.

Каждую попытку вычислить корень из -1 придётся обрабатывать отдельно. Это кажется неудобным, но
в этом и заключается смысл — каждое место где вы ждёте ислючение нужно помещать в свой
try except блок.

Можно обработать исключение так:

try:
while guess * guess != x and i < 20:
guess = (guess + x / guess) / 2.0
i += 1
except ZeroDivisionError:
raise ValueError()
return guess

def main():
print(sqrt(9))
print(sqrt(-1))

python sqrt_ex.py

3.0
Traceback (most recent call last):
File «/home/andrei/sqrt_ex3.py», line 17, in sqrt
guess = (guess + x / guess) / 2.0
ZeroDivisionError: float division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File «/home/andrei/sqrt_ex3.py», line 30, in <module>
main()
File «/home/andrei/sqrt_ex3.py», line 25, in main
print(sqrt(-1))
File «/home/andrei/sqrt_ex3.py», line 20, in sqrt
raise ValueError()
ValueError

Гораздо логичнее поднимать исключение сразу при получении аргумента

def sqrt(x):
«»»Compute square roots using the method
of Heron of Alexandria.

Args:
x: The number for which the square root
is to be computed.

Returns:
The square root of x.

Raises:
ValueError: If x is negative
«»»

if x < 0:
raise ValueError(
«Cannot compute square root of «
f«negative number {x}»)

guess = x
i = 0
while guess * guess != x and i < 20:
guess = (guess + x / guess) / 2.0
i += 1
return guess

def main():
print(sqrt(9))
print(sqrt(-1))
print(sqrt(2))
print(sqrt(-1))

if __name__ == ‘__main__’:
main()

python sqrt_ex.py

3.0
Traceback (most recent call last):
File «/home/avorotyn/python/lessons/pluralsight/core_python_getting_started/chapter8/sqrt_ex4.py», line 35, in <module>
main()
File «/home/avorotyn/python/lessons/pluralsight/core_python_getting_started/chapter8/sqrt_ex4.py», line 30, in main
print(sqrt(-1))
File «/home/avorotyn/python/lessons/pluralsight/core_python_getting_started/chapter8/sqrt_ex4.py», line 17, in sqrt
raise ValueError(
ValueError: Cannot compute square root of negative number -1

Пока получилось не очень — виден Traceback

Убрать Traceback можно добавив обработку ValueError в вызов функций

import sys

def sqrt(x):
«»»Compute square roots using the method
of Heron of Alexandria.

Args:
x: The number for which the square root
is to be computed.

Returns:
The square root of x.

Raises:
ValueError: If x is negative
«»»

if x < 0:
raise ValueError(
«Cannot compute square root of «
f«negative number {x}»)

guess = x
i = 0
while guess * guess != x and i < 20:
guess = (guess + x / guess) / 2.0
i += 1
return guess

def main():
try:
print(sqrt(9))
print(sqrt(2))
print(sqrt(-1))
print(«This is never printed»)
except ValueError as e:
print(e, file=sys.stderr)

print(«Program execution continues normally here.»)

if __name__ == ‘__main__’:
main()

python sqrt_ex.py

3.0
1.414213562373095
Cannot compute square root of negative number -1
Program execution continues normally here.

Исключения, которые не нужно обрабатывать

IndentationError, SyntaxError, NameError нужно исправлять в коде а не пытаться обработать.

Важно помнить, что использовать обработку исключений для замалчивания ошибок программиста недопустимо.

Список исключений

Список встроенных в Python исключений

Существуют следующие типы объектов Exception

BaseException
+— SystemExit
+— KeyboardInterrupt
+— GeneratorExit
+— Exception
+— StopIteration
+— StopAsyncIteration
+— ArithmeticError
| +— FloatingPointError
| +— OverflowError
| +— ZeroDivisionError
+— AssertionError
+— AttributeError
+— BufferError
+— EOFError
+— ImportError
| +— ModuleNotFoundError
+— LookupError
| +— IndexError
| +— KeyError
+— MemoryError
+— NameError
| +— UnboundLocalError
+— OSError
| +— BlockingIOError
| +— ChildProcessError
| +— ConnectionError
| | +— BrokenPipeError
| | +— ConnectionAbortedError
| | +— ConnectionRefusedError
| | +— ConnectionResetError
| +— FileExistsError
| +— FileNotFoundError
| +— InterruptedError
| +— IsADirectoryError
| +— NotADirectoryError
| +— PermissionError
| +— ProcessLookupError
| +— TimeoutError
+— ReferenceError
+— RuntimeError
| +— NotImplementedError
| +— RecursionError
+— SyntaxError
| +— IndentationError
| +— TabError
+— SystemError
+— TypeError
+— ValueError
| +— UnicodeError
| +— UnicodeDecodeError
| +— UnicodeEncodeError
| +— UnicodeTranslateError
+— Warning
+— DeprecationWarning
+— PendingDeprecationWarning
+— RuntimeWarning
+— SyntaxWarning
+— UserWarning
+— FutureWarning
+— ImportWarning
+— UnicodeWarning
+— BytesWarning
+— EncodingWarning
+— ResourceWarning

IndexError

Пример

>>> a = [0, 1, 2]
>>> a[3]

Traceback (most recent call last):
File «<stdin>», line 1, in <module>
IndexError: list index out of range

ValueError

ValueError поднимается когда объект правильного типа, но содержит неправильное значение

>>> int(«text»)

Traceback (most recent call last):
File «<stdin>», line 1, in <module>
ValueError: invalid literal for int() with base 10: ‘text’

KeyError

KeyError поднимается когда поиск по ключам не даёт результата

>>> sites = dict(urn=1, heihei=2, eth1=3)
>>> sites[«topbicycle»]

Traceback (most recent call last):
File «<stdin>», line 1, in <module>
KeyError: ‘topbicycle’

TypeError

TypeError поднимается когда для успешного выполнения операции нужен объект
определённого типа, а предоставлен другой тип.

pi = 3.1415

text = «Pi is approximately « + pi

python str_ex.py

Traceback (most recent call last):
File «str_ex.py», line 3, in <module>
text = «Pi is approximately » + pi
TypeError: can only concatenate str (not «float») to str

Пример из статьи

str()

SyntaxError

SyntaxError поднимается когда допущена ошибка в синтаксисе языка, например, использован
несуществующий оператор.

Python 3.8.10 (default, Nov 14 2022, 12:59:47)
[GCC 9.4.0] on linux
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>>>
>>>
>>> 0 <> 0
File «<stdin>», line 1
0 <> 0
^
SyntaxError: invalid syntax

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__future__

Sometimes, a Python script comes across an unusual situation that it can’t handle, and the program gets terminated or crashes. In this article, we’ll learn How to catch and print exception messages in Python which can help us better understand and debug such errors.

Common Examples of Exception Messages

The most common example of an exception is a “FileNotFoundError” which is raised when you’re importing a file, but it doesn’t exist. Similarly, dividing a number by zero gives a “ZeroDivisionError” and displays a system-generated error message. All these run-time errors are known as exceptions. These exceptions should be caught and reported to prevent the program from being terminated.

In Python, exceptions are handled with the (try… except) statement. The statements which handle the exceptions are placed in the except block whereas the try clause includes the expressions which can raise an exception. Consider an example in which you take a list of integers as input from the user.

# Creating an empty list
new_list =[]

n = int(input("Enter number of elements : "))

for i in range(n):

    item = int(input())

    # Add the item in the list
    new_list.append(item)

print(new_list)

The program shown above takes integers as input and creates a list of these integers. If the user enters any character, the program will crash and generate the following output.

Output:

Enter number of elements : 7
23
45
34
65
2a
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-1-ac783af2c9a3> in <module>()
      3 n = int(input("Enter number of elements : "))
      4 for i in range(n):
----> 5     item = int(input())
      6     # Add the item in the list
      7     new_list.append(item)

ValueError: invalid literal for int() with base 10: '2a'

Different Methods to catch Exception messages

1) Using the Try and Except block

The first method to catch and print the exception messages in Python is by using except and try statements. If the user enters anything except the integer, we want the program to skip that input and move to the next value. In this way, our program will not crash and will catch and print the exception message. This can be done using try and except statements. Inside the try clause, we’ll take input from the user and append it to “new_list” variable. If the user has entered any input except integers mistakenly, the except block will print “Invalid entry” and move towards the next value. In this way, the program continues to run and skip the invalid entries.

# Creating an empty list
new_list =[]

n = int(input("Enter number of elements : "))

for i in range(n):

  try:
    item = int(input())

    # Add the item in the list
    new_list.append(item)

  except:

    print("Invalid Input!")

    print("Next entry.")

print("The list entered by user is: ", new_list)

Output:

Enter number of elements : 7
65
43
23
4df
Invalid Input!
Next entry.
76
54
90
The list entered by user is:  [65, 43, 23, 76, 54, 90]

There are various methods to catch and report these exceptions using try and except block. Some of them are listed below along with examples.

Catching and Reporting/Print exceptions messages in Python

This is the second method to catch and print the exception messages in Python. With the help of the print function, you can capture, get and print an exception message in Python. Consider an example in which you have a list containing elements of different data types. You want to divide all the integers by any number. This number on division with the string datatypes will raise “TypeError” and the program will terminate if the exceptions are not handled. The example shown below describes how to handle this problem by capturing the exception using the try-except block and reporting it using the print command.

list_arr=[76,65,87,"5f","7k",78,69]

for elem in list_arr:

  try:

    print("Result: ", elem/9)

  except Exception as e:

    print("Exception occurred for value '"+ elem + "': "+ repr(e))

Result:  8.444444444444445
Result:  7.222222222222222
Result:  9.666666666666666
Exception occurred for value '5f': TypeError("unsupported operand type(s) for /: 'str' and 'int'")
Exception occurred for value '7k': TypeError("unsupported operand type(s) for /: 'str' and 'int'")
Result:  8.666666666666666
Result:  7.666666666666667

print an Error message using try and logger.exception

Another method is to use logger.exception() which produces an error message as well as the log trace, which contains information such as the code line number at which the exception occurred and the time the exception occurred. This logger.exception() method should be included within the except statement; otherwise, it will not function properly.

import logging

logger=logging.getLogger()

num1=int(input("Enter the number 1:"))

num2=int(input("Enter the number 2:"))

try: 

  print("Result: ", num1/num2)

except Exception as e:

  logger.exception("Exception Occured while code Execution: "+ str(e))

Enter the number 1:82
Enter the number 2:4
Result:  20.5

Suppose a user enters 0 in the 2nd number, then this will raise a “ZeroDivisionError” as shown below.

Enter the number 1:9
Enter the number 2:0
Exception Occured while code Execution: division by zero
Traceback (most recent call last):
  File "<ipython-input-27-00694f615c2f>", line 11, in <module>
    print("Result: ", num1/num2)
ZeroDivisionError: division by zero

Similarly, if you’ve two lists consisting of integers and you want to create a list consisting of results obtained by dividing list1 with list2. Suppose you don’t know whether the two lists consist of integers or not.

import logging

logger=logging.getLogger()

list1=[45, 32, 76, 43, 0, 76]

list2=[24, "world", 5, 0, 4, 6]

Result=[]

for i in range(len(list1)):

  try:

    Result.append(list1[i]/list2[i])

  except Exception as e:

    logger.exception("Exception Occured while code Execution: "+ str(e))

print(Result)

In this example, “world” in the 2nd index of list2 is a string and 32 on division with a string would raise an exception. But, we have handled this exception using try and except block. The logger.exception() command prints the error along with the line at which it occurred and then moves toward the next index. Similarly, all the values are computed and stored in another list which is then displayed at the end of the code.

Exception Occured while code Execution: unsupported operand type(s) for /: 'int' and 'str'
Traceback (most recent call last):
  File "<ipython-input-1-5a40f7f6c621>", line 8, in <module>
    Result.append(list1[i]/list2[i])
TypeError: unsupported operand type(s) for /: 'int' and 'str'
Exception Occured while code Execution: division by zero
Traceback (most recent call last):
  File "<ipython-input-1-5a40f7f6c621>", line 8, in <module>
    Result.append(list1[i]/list2[i])
ZeroDivisionError: division by zero
[1.875, 15.2, 0.0, 12.666666666666666]

The logger module has another function “logger.error()” which returns only an error message. The following example demonstrates how the logger.error() function may be used to capture exception messages in Python. In this example, we have just replaced logger.exception in the above example with logger.error() function

import logging

logger=logging.getLogger()

list1=[45, 32,76,43,0, 76]

list2=[24, "world", 5, 0, 4, 6]

Result=[]

for i in range(len(list1)):

  try:

    Result.append(list1[i]/list2[i])

  except Exception as e:

    logger.error("Exception Occured while code Execution: "+ str(e))

print(Result)

Output:

Exception Occured while code Execution: unsupported operand type(s) for /: 'int' and 'str'
Exception Occured while code Execution: division by zero
[1.875, 15.2, 0.0, 12.666666666666666]

Catching and printing Specific Exception messages

The previous section was all about how to catch and print exceptions. But, how will you catch a specific exception such as Valueerror, ZeroDivisionError, ImportError, etc? There are two cases if you want to catch one specific exception or multiple specific exceptions. The following example shows how to catch a specific exception.

a = 'hello'

b = 4

try:

    print(a + b)

except TypeError as typo:

    print(typo)

Output:

can only concatenate str (not "int") to str

Similarly, if you want to print the result of “a/b” also and the user enters 0 as an input in variable “b”, then the same example would not be able to deal with ZeroDivisionError. Therefore we have to use multiple Except clauses as shown below.

a = 6

b = 0

try:

    print(a + b)

    print(a/b)

except TypeError as typo:

    print(typo)

except ZeroDivisionError as zer:

    print(zer)

The same code is now able to handle multiple exceptions.

6
division by zero

To summarize, all of the methods described above are effective and efficient. You may use any of the methods listed above to catch and print the exception messages in Python depending on your preferences and level of comfort with the method. If you’ve any queries regarding this article, please let us know in the comment section. Your feedback matters a lot to us.