Python Traceback

# Python program to demonstrate
# traceback


mylist = [1, 2, 3]
print(mylist[10])

Traceback (most recent call last):
  File "", line 2, in 
print(mylist[10])
IndexError: list index out of range

How to read traceback

• GREEN BOX shows the what type of error occurred .
• BLUE BOX shows the relevant information about error
• ORANGE BOX shows traceback statement for recent calls, below The firstRuntime Error: Traceback (most recent call last): File "", line 1, in ModuleNotFoundError: No module named 'asdf' line of each call contains information like the file name, line number, and module name
• RED underlined part shows exact line where exception occurred.

• NameError
• IndexError
• KeyError
• TypeError
• valueError
• ImportError /ModuleNotFound

1. NameError: NameError occurs when you try to reference some variable which hasn’t been defined in the code. Example: Python3

   number = 1 
   
   # since no numb variable is
   # defined it will give NameError.
   print(numb)  
   

   Output:

   Traceback (most recent call last):
     File "gfg.py", line 5, in 
       print(numb)  
   NameError: name 'numb' is not defined
   

2. IndexError: An IndexError is raised when a sequence is referenced which is out of range. Example: Python3

   mylist = [1, 2, 3]
   
   # Accessing the index out
   # of range will raise IndexError
   print(mylist[10])
   

   Output:

   Traceback (most recent call last):
     File "gfg.py", line 5, in 
       print(mylist[10])
   IndexError: list index out of range
   

3. KeyError: Similar to the IndexError, the KeyError is raised when you attempt to access a key that isn’t in the mapping, usually in the case of Python dict. Think of this as the IndexError but for dictionaries. Example: Python3

   DICT ={ "a" :25, "b" :65 }
   
   # A is not mapped in dict
   # will raise KeyError
   print(DICT["A"])
   

   Output:

   Traceback (most recent call last):
     File "gfg.py", line 5, in 
       print(DICT["A"])
   KeyError: 'A'
   

4. TypeError: TypeError is raised when an operation or function is applied to an object of inappropriate type. This exception returns a string giving details about the type mismatch. Example: Python3

   c = 'b'+3
   print(c)
   

   Output:

   Traceback (most recent call last):
     File "gfg.py", line 1, in 
       c = 'b'+3
   TypeError: must be str, not int
   

5. ValueError: A ValueError is raised when a built-in operation or function receives an argument that has the right type but an invalid value. Example: Python3

   print(int('xyz'))
   

   Traceback (most recent call last):
     File "gfg.py", line 1, in 
       print(int('xyz'))
   ValueError: invalid literal for int() with base 10: 'xyz'
   

6. ImportError: The ImportError is raised when something goes wrong with an import statement. You’ll get this exception, or its subclass ModuleNotFoundError, if the module you are trying to import can’t be found or if you try to import something from a module that doesn’t exist in the module. Example: Python3

   import module_does_not_exist
    
   

   Traceback (most recent call last):
     File "gfg.py", line 1, in 
       import module_does_not_exist
   ModuleNotFoundError: No module named 'module_does_not_exist'