Python – Error Types
The most common reason of an error in a Python program is when a certain statement is not in accordance with the prescribed usage. Such an error is called a syntax error. The Python interpreter immediately reports it, usually along with the reason.
IndexError is thrown when trying to access an item at an invalid index.
>>> L1=[1,2,3]
>>> L1[3]
Traceback (most recent call last):
File “<pyshell#18>”, line 1, in <module>
L1[3]
IndexError: list index out of range
ModuleNotFoundError is thrown when a module could not be found.
>>> import notamodule
Traceback (most recent call last):
File “<pyshell#10>”, line 1, in <module>
import notamodule
ModuleNotFoundError: No module named ‘notamodule’
KeyError is thrown when a key is not found.
>>> D1={‘1’:”aa”, ‘2’:”bb”, ‘3’:”cc”}
>>> D1[‘4’]
Traceback (most recent call last):
File “<pyshell#15>”, line 1, in <module>
D1[‘4’]
KeyError: ‘4’
ImportError is thrown when a specified function can not be found.
>>> from math import cube
Traceback (most recent call last):
File “<pyshell#16>”, line 1, in <module>
from math import cube
ImportError: cannot import name ‘cube’
StopIteration is thrown when the next()
function goes beyond the iterator items.
>>> it=iter([1,2,3])
>>> next(it)
1
>>> next(it)
2
>>> next(it)
3
>>> next(it)
Traceback (most recent call last):
File “<pyshell#23>”, line 1, in <module>
next(it)
StopIteration
TypeError is thrown when an operation or function is applied to an object of an inappropriate type.
>>> ‘2’+2
Traceback (most recent call last):
File “<pyshell#23>”, line 1, in <module>
‘2’+2
TypeError: must be str, not int
ValueError is thrown when a function’s argument is of an inappropriate type.
>>> int(‘xyz’)
Traceback (most recent call last):
File “<pyshell#14>”, line 1, in <module>
int(‘xyz’)
ValueError: invalid literal for int() with base 10: ‘xyz’
NameError is thrown when an object could not be found.
>>> age
Traceback (most recent call last):
File “<pyshell#6>”, line 1, in <module>
age
NameError: name ‘age’ is not defined
ZeroDivisionError is thrown when the second operator in the division is zero.
>>> x=100/0
Traceback (most recent call last):
File “<pyshell#8>”, line 1, in <module>
x=100/0
ZeroDivisionError: division by zero
KeyboardInterrupt is thrown when the user hits the interrupt key (normally Control-C) during the execution of the program.
>>> name=input(‘enter your name’)
enter your name^c
Traceback (most recent call last):
File “<pyshell#9>”, line 1, in <module>
name=input(‘enter your name’)
KeyboardInterrupt
The following table lists important built-in exceptions in Python.
Exception | Description |
---|---|
AssertionError | Raised when the assert statement fails. |
AttributeError | Raised on the attribute assignment or reference fails. |
EOFError | Raised when the input() function hits the end-of-file condition. |
FloatingPointError | Raised when a floating point operation fails. |
GeneratorExit | Raised when a generator’s close() method is called. |
ImportError | Raised when the imported module is not found. |
IndexError | Raised when the index of a sequence is out of range. |
KeyError | Raised when a key is not found in a dictionary. |
KeyboardInterrupt | Raised when the user hits the interrupt key (Ctrl+c or delete). |
MemoryError | Raised when an operation runs out of memory. |
NameError | Raised when a variable is not found in the local or global scope. |
NotImplementedError | Raised by abstract methods. |
OSError | Raised when a system operation causes a system-related error. |
OverflowError | Raised when the result of an arithmetic operation is too large to be represented. |
ReferenceError | Raised when a weak reference proxy is used to access a garbage collected referent. |
RuntimeError | Raised when an error does not fall under any other category. |
StopIteration | Raised by the next() function to indicate that there is no further item to be returned by the iterator. |
SyntaxError | Raised by the parser when a syntax error is encountered. |
IndentationError | Raised when there is an incorrect indentation. |
TabError | Raised when the indentation consists of inconsistent tabs and spaces. |
SystemError | Raised when the interpreter detects internal error. |
SystemExit | Raised by the sys.exit() function. |
TypeError | Raised when a function or operation is applied to an object of an incorrect type. |
UnboundLocalError | Raised when a reference is made to a local variable in a function or method, but no value has been bound to that variable. |
UnicodeError | Raised when a Unicode-related encoding or decoding error occurs. |
UnicodeEncodeError | Raised when a Unicode-related error occurs during encoding. |
UnicodeDecodeError | Raised when a Unicode-related error occurs during decoding. |
UnicodeTranslateError | Raised when a Unicode-related error occurs during translation. |
ValueError | Raised when a function gets an argument of correct type but improper value. |
ZeroDivisionError | Raised when the second operand of a division or module operation is zero. |