Common Errors and Messages

Here are some common Python errors  and error  messages to look  out for. Please let us give if you have any favorite additions for this list.

• A problem about NoneType often means you forgot a return.

def plus1 (x):

x + 1

>>> y = plus1(x)

>>> plus1(x) + 2

Traceback (most recent call last):

File "", line 1, in

TypeError that shows: unsupported operator type(s) for +: 'NoneType' and 'int'

• Weird results from math can give from integer division

>>> 3/ 9

0

• "Unsubscriptable object" seems you are trying to get an element out of something that isn't a dictionary, list, or tuple.

>>> x = 1

>>> x[3]

Traceback (most recent call last):

File "", line 1, in

TypeError that shows: 'int' object is unsubscriptable

• "Object is not callable" defines that you are trying to use something that isn't a procedure or method as if it were.

>>> x = 1

>>> x(3)

Traceback (most recent call last):

File "", line 1, in

TypeError that shows: 'int' object is not callable

• "List index out of range" describes that you are trying to read or write an element of a list that is not present.

>>> a = range(5)

>>> a

[0, 1, 2, 3, 4]

>>> a[5]

Traceback (most recent call last):

File "", line 1, in

IndexError that shows: list index out of range

• "Maximum recursion depth exceeded" produces the error has a recursive procedure that is nested your parent case is not being reached due to a bug.

def fizz(x):

return fizz(x - 1)

>>> fizz(10)

Traceback (most recent call last): File "", line 1, in File "", line 2, in fizz

File "", line 2, in fizz

...

File "", line 2, in fizz

RuntimeError that shows message: maximum recursion depth exceeded

• "Key Error " defines that you are trying to look up an element in a dictionary that is not present.

>>> d = {'a':7, 'b':8}

>>> d['c']

Traceback (most recent call last):

File "", line 1, in

KeyError: 'c'

• Another common error is forgetting the self before calling a function. This creates the same error that you would get if you tried to call a function that wasn't de?ned at all.

Traceback (most recent call last): File "", line 1, in File "V2.py", line 22, in  

add    

return add(v)

NameError: global name 'add' is not defined