When you say «name» this could mean a couple of things: it could mean only the «immediate» classname, or it could mean the fully qualified name. Usually the latter will be much more useful and less error-prone: I’ve come across more than one case of 2 or more types with same «immediate» classname but from different packages.
If you want to print or log the fully qualified name this is one of the simplest things to do:
try:
do_something()
except BaseException as e:
logger.error(f'whoops! {type(e)}: {e}')
# or maybe
print(f'whoops! {type(e)}: {e}', file=sys.stderr)
The fully qualified classname will then be printed out like this: «<class ‘json.decoder.JSONDecodeError’>», and then be followed by the exception message. The OP says he wants «for example», to print a message, so assert statements as in the chosen answer don’t seem to be called for.
The answer by MrName is also not irrelevant, and does make a sensible suggestion! if in the above you replaced logger.error(...) with logger.exception('whoops!') (NB a user message is a required param) you’d get your exception’s fully qualified name logged, not to mention its message, and a stack trace for free.
PS as suggested by the name, JSONDecodeError in my example is an Error, not an Exception (it is a subclass of ValueError). Catching BaseException (the superclass of both Error and Exception) usually makes life easier when you’re not fishing for a specific exception. The OP says he wants to catch «all» exceptions.
In this article, let us learn about printing error messages from Exceptions with the help of 5 specifically chosen examples.
I have divided this article into 2 major sections
- Printing custom error messages and
- Printing a specific part of the default error message. By “default error message“, I mean the error message that you typically get in the command line if you did not catch a given exception)
Depending on which of the 2 options above you are looking for, you can jump to the respective section of the article using the table of content below.
So, let’s begin!
Printing Custom Error messages
There are 3 ways to print custom error messages in Python. Let us start with the simplest of the 3, which is using a print() statement.
Option#1: Using a simple print() statement
The first and easiest option is to print error messages using a simple print() statement as shown in the example below.
try:
#Some Problematic code that can produce Exceptions
x = 5/0
except Exception as e:
print('A problem has occurred from the Problematic code: ', e)Running this code will give the output below.
A problem has occurred from the Problematic code: division by zeroHere the line “x = 5/0″ in Example 1 above raised a “ZeroDivisionError” which was caught by our except clause and the print() statement printed the default error message which is “division by zero” to the standard output.
One thing to note here is the line “except Exception as e“. This line of code’s function is to catch all possible exceptions, whichever occurs first as an “Exception” object. This object is stored in the variable “e” (line 4), which returns the string ‘division by zero‘ when used with the print() statement (line 5).
To summarize if you wish to print out the default error message along with a custom message use Option#1.
This is the simplest way to print error messages in python. But this option of putting your custom messages into print statements might not work in cases where you might be handling a list of exceptions using a single except clause. If you are not exactly sure how to catch a list of exceptions using a single except clause, I suggest reading my other article in the link below.
Python: 3 Ways to Catch Multiple Exceptions in a single “except” clause
There I have explained the 3 ways through which you can catch a list of exceptions along with tips on when is the right situation to catch each of these exceptions.
Now that we have learned how to print the default string which comes with an exception object, let us next learn how to customize the message that e carried (the string ‘division by zero‘) and replace that with our own custom error message.
Option#2: Using Custom Exception classes to get customized error messages
In Python, you can define your own custom exception classes by inheriting from another Exception class as shown in the code below.
class MyOwnException(Exception):
def __str__(self):
return 'My Own Exception has occurred'
def __repr__(self):
return str(type(self))
try:
raise MyOwnException
except MyOwnException as e:
print(e)
print(repr(e))How to choose the exception class to inherit from?
In the above example, I have inherited from the Exception class in python, but the recommended practice is to choose a class that closely resembles your use-case.
For example, say you are trying to work with a string type object and you are given a list type object instead, here you should inherit your custom exception from TypeError since this Exception type closely resembles your use case which is “the variable is not of expected type”.
If you are looking for getting an appropriate Exception class to inherit from, I recommend having a look at all the built-in exceptions from the official python page here. For the sake of keeping this example simple, I have chosen the higher-level exception type named “Exception” class to inherit from.
In the code below, we are collecting values from the user and to tell the user that there is an error in the value entered we are using the ValueError class.
class EnteredGarbageError(ValueError):
def __str__(self):
return 'You did not select an option provided!'
try:
options = ['A', 'B', 'C']
x = input('Type A or B or C: ')
if x not in options:
raise EnteredGarbageError
else:
print ('You have chosen: ', x)
except EnteredGarbageError as err:
print(err)Now that we understand how to choose a class to inherit from, let us next have a look at how to customize the default error messages that these classes return.
How to customize the error message in our custom exception class?
To help us achieve our purpose here which is to print some custom error messages, all objects in python come with 2 methods named __str__ and __repr__. This is pronounced “dunder-str” and “dunder-repr” where “dunder” is short for “double underscore”.
Dunder-str method:
The method __str__ returns a string and this is what the built-in print() function calls whenever we pass it an object to print.
print(object1)In the line above, python will call the __str__ method of the object and prints out the string returned by that method.
Let us have a look at what python’s official documentation over at python.org has to say about the str method.
In simpler words, the str method returns a human-readable string for logging purposes, and when this information is passed to the built-in function print(), the string it returns gets printed. So since our implementation of str returns the string “My Own Exception has occurred” this string got printed on the first line of the exception message. Dunder-repr method: __repr__ is another method available in all objects in python. Where it differs from the dunder-str method is the fact that while the __str__ is used for getting a “friendly message”, the __repr__ method is used for getting, a more of a, “formal message”. You can think of str as a text you got from your friends and repr as a notice you got from a legal representative! The below screenshot from python’s official documentation explains the use of __repr__ method.
Again, in simpler words, repr is typically used to print some “formal” or “official” information about an object in Python
In our Example 2 above, the repr method returned the class name using the built-in type() function.
Next, let us see another variation where we can print different error messages using a single Exception class without making a custom class.
Option#3: Custom Error messages from the raise statement
try:
raise Exception('I wish to print this message')
except Exception as error:
print(error)Lucky for us, python has made this process incredibly simple! Just pass in the message as an argument to the type of exception you wish to raise and this will print that custom message instead!
In the above code, we are throwing an exception of type “Exception” by calling its constructor and giving the custom message as an argument, which then overrides the default __str__ method to return the string passed in.
If you wish to learn more about raise statement, I suggest reading my other article in the link below
Python: Manually throw/raise an Exception using the “raise” statement
where I have explained 3 ways you can use the raise statement in python and when to use each.
But when to use option 2 and when to use option 3?
On the surface, Option#3 of passing in the custom message may look like it made option#2 of using custom classes useless. But the main reason to use Option#2 is the fact that Option#2 can be used to override more than just the __str__ method.
Let’s next move on to section 2 of this article and look at how to choose a specific part of the default error message (the error printed on the console when you don’t catch an exception) and use that to make our own error messages
Choosing Parts of Default Error Messages to print
To understand what I mean by “Default Error Message” let us see an example
raise ValueError("This is an ValueError")This line when run, will print the following error message
Traceback (most recent call last):
File "<ipython-input-24-57127e33a735>", line 1, in <module>
raise ValueError("This is an ValueError")
ValueError: This is an ValueErrorThis error message contains 3 Parts
- Exception Type (ValueError)
- Error message (This is an ValueError)
- and the stack trace (the 1st few lines showing us where exactly in the program the exception has occurred)
The information needed
- to extract and use each of the individual pieces of information listed above and
- when to use what piece of information
is already covered with the help of several examples in my previous article in the link below
Python Exceptions: Getting and Handling Error Messages as strings.
And with that I will end this article!
If you are looking for another interesting read, try the article in the link below.
Exceptions in Python: Everything You Need To Know!
The above article covers all the basics of Exception handling in Python like
- when and how to ignore exceptions
- when and how to retry the problematic code that produced the exception and
- when and how to log the errors
I hope you enjoyed reading this article and got some value from it.
Feel free to share it with your friends and colleagues!
How to get the name of an exception that was caught in Python
Ссылка на оверфло
Три варианта:
type(exception).__name__exception.__class__.__name__exception.__class__.__qualname__
Пример реализации
try:
foo = bar
except Exception as exception:
assert type(exception).__name__ == 'NameError'
assert exception.__class__.__name__ == 'NameError'
assert exception.__class__.__qualname__ == 'NameError'
Смотри в дополнение про то, как получить сообщение ошибки в виде строки [2021-06-04-daily-note]
Feature Launch: Import scripts into notebook kernels
Скажем так, не сильно полезная фича, т.к. нет возможности выстроить настоящую структуру пакета, а импорт ограничивается ноутом. Ну и плюс все это надо делать руками через jupyter notebook. Но, если есть какие-то сильно часто встречающиеся куски кода, то можно попробовать так реализовать.
- Create a script kernel with the code you’d like to import.
- Under the “File” menu, click on “Make Utility Script”. This will let you import this script to notebook kernels.
- Commit your script. When you import a script, you’re importing the most recent committed version. If you haven’t committed a version yet, you won’t see it in the list of scripts you can import.
- Open the notebook where you’d like to import the script.
- Add the script. Under “File”, click “Add utility script”. Search for the script you want and click to add it. You should see it listed under “usr/lib” in the panel on the right hand side.
- Import your script. In Python you can do this using
import nameof_script. -
Use the functions or objects you’ve imported!
- a utility script can be a combination of multiple code snippets in different source files
- be able to add data/non-code related files as part of the utility function
- allow folder structure where code and data can reside in a structured fashion
- allow access to the data area of the notebook via an environment variable or some other method
- allow linking a gist where the code can reside (gist will contain the code for the utility script)
- allow linking a git repo (via branch or commit points) — will contain the code for the utility script)
- allow linking only a folder in a git repo where the code and data resides
The above will help in the following ways:
- keep the main utility script small, simple and modular
- easy to read, change and use
- can be version controlled via another public SCM system while still visible to the kernel
- keep components of the utility script separate from the data or configuration files in an organised manner
Какое-то там обсуждение на эту тему
If a python code throws an exception, we can catch it and print the type, the error message, traceback and get information like file name and line number in python script where the exception occurred.
We can find the type, value, traceback parameters of the error
Type gives the type of exception that has occurred; value contains error message; traceback contains stack snapshot and many other information details about the error message.
The sys.exc_info() function returns a tuple of these three attributes, and the raise statement has a three-argument form accepting these three parts.
Getting exception type, file number and line number in sample code
import sys, os
try:
raise NotImplementedError("No error")
except Exception as e:
exc_type, exc_obj, exc_tb = sys.exc_info()
fname = os.path.split(exc_tb.tb_frame.f_code.co_filename)[1]
print(exc_type, fname, exc_tb.tb_lineno
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. If you want to learn more about Python Programming, visit Python Tutorials.
In Python, you can catch and print exception messages in two ways: using “try-except” statements or “logger.exception()”. With “try-except”, wrap the code in a try block, then use “except Exception as e” to catch the exception and save its message in variable e. Print it using “print(e)” or process it further. “logger.exception()” provides error message and trace information like line number and time.
The most common example is a “FileNotFoundError” 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'Use Except and Try statement to catch and print the Exception and save its Error Messages
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)
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.
eXAMPLE 1:
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: 7.666666666666667Using try and logger.exception to print an Error message
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: 20.5Suppose 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 zeroSimilarly, 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.
EXAMPLE 2:
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
EXAMPLE 3:
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 Exceptions 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.
EXAMPLE 4:
a = 'hello'
b = 4
try:
print(a + b)
except TypeError as typo:
print(typo)
Output:
can only concatenate str (not "int") to strSimilarly, 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.
EXAMPLE 5:
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 zeroTo 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.