16.1. Exception About

Important

Used when error occurs
You can catch exception and handles erroneous situation
If file does not exists
If no permissions to read file
If function argument is invalid type (ie. int('one'))
If value is incorrect (ie. negative Kelvin temperature)
If network or database connection could not be established

16.1.1. NameError

Local or global name is not found

✘>>> print(firstname)
Traceback (most recent call last):
NameError: name 'firstname' is not defined

16.1.2. IndexError

Sequence subscript is out of range

✘>>> data = ['Mark', 'Melissa', 'Rick']
>>>
>>> data[10]
Traceback (most recent call last):
IndexError: list index out of range

16.1.3. KeyError

Dictionary key is not found

✘>>> data = {'firstname': 'Mark', 'lastname': 'Watney'}
>>>
>>> data['age']
Traceback (most recent call last):
KeyError: 'age'

16.1.4. SyntaxError

Parser encounters a syntax error

✘>>> if True
...     print('Mark')
...
Traceback (most recent call last):
SyntaxError: expected ':'

16.1.5. IndentationError

Syntax errors related to incorrect indentation

✘>>> if True:
...     print('Mark')
...      print('Melissa')
...     print('Rick')
...
Traceback (most recent call last):
IndentationError: unexpected indent

16.1.6. ValueError

Argument has an invalid value

✘>>> float('1')
1.0

✘>>> float('one')
Traceback (most recent call last):
ValueError: could not convert string to float: 'one'

16.1.7. TypeError

Operation or function is applied to an object of inappropriate type

✘>>> data = ['Mark', 'Melissa', 'Rick']
>>>
>>> float(data)
Traceback (most recent call last):
TypeError: float() argument must be a string or a real number, not 'list'

16.1.8. AttributeError

Attribute reference or assignment fails

✘>>> data = ('Mark', 'Melissa', 'Rick')
>>>
>>> data.append('Alex')
Traceback (most recent call last):
AttributeError: 'tuple' object has no attribute 'append'

16.1.9. IsADirectoryError

Trying to open directory instead of file

✘>>> open('/tmp')
Traceback (most recent call last):
IsADirectoryError: [Errno 21] Is a directory: '/tmp'

16.1.10. FileNotFoundError

File does not exists

✘>>> open('myfile.txt')
Traceback (most recent call last):
FileNotFoundError: [Errno 2] No such file or directory: 'myfile.txt'

16.1.11. ModuleNotFoundError

Module could not be located

✘>>> import nasa
Traceback (most recent call last):
ModuleNotFoundError: No module named 'nasa'

Note, that this exception is also raised when you don't have this module installed. Such as while importing pandas or numpy without installing it first.

16.1.12. ZeroDivisionError

Division or modulo by zero

✘>>> 1 / 0
Traceback (most recent call last):
ZeroDivisionError: division by zero

✘>>> data = []
>>>
>>> mean = sum(data) / len(data)
Traceback (most recent call last):
ZeroDivisionError: division by zero

16.1.13. KeyboardInterrupt

User interrupts program execution
Usually by pressing Ctrl+C
PyCharm: Stop button in the Python Console toolbar

While running the following code, you can interrupt it by pressing Ctrl+C:

✘>>>
... while True:
...     pass
...
Traceback (most recent call last):
KeyboardInterrupt