List and tuple reference

Sequences: a quick reference guide

Mutability and immutability

Type	Mutable	Indexed read	Indexed write
list	yes	yes	yes
tuple	no	yes	no
str	no	yes	no

Built-ins

Type	len()	sum()	min() and max()
list	yes	yes (if numeric)	yes, with some restrictions
tuple	yes	yes (if numeric)	yes, with some restrictions
str	yes	no	yes

Methods

Type	.sort(), .append(), and .pop()	.index()
list	yes	yes
tuple	no	yes
str	no	yes

• If an object is mutable, then the object can be modified.
• Indexed read: m[i] where m is a list or tuple, and i is a valid index into the list or tuple.
• Indexed write: m[i] on left-hand side of assignment.
• Python built-in len() works the same for lists and tuples.
• Python built-ins sum(), min(), and max() behave the same for lists and tuples.
• For sum() to work m must contain only numeric types (int, float) or Booleans. So, for example, sum([1, 1.0, True]) yields three. We cannot sum over strings.
• min() and max() work so long as the elements of the list or tuple are comparable—meaning that >, >=, <, <=, == can be applied to any pair of list elements. We cannot compare numerics and strings, but we can compare numerics with numerics and strings with strings.
• We can test whether a value is in a list or tuple with in. For example 'cheese' in m returns a Boolean.
• m.sort(), m.append(), and m.pop() work for lists only. Tuples are immutable. Note that these change the list in place.
• We cannot apply m.sort() if the list or tuple contains elements which are not comparable.
• We must supply an argument to m.append() (we have to append something).
• m.pop() without argument pops the last element from a list.
• m.pop(i) where i is a valid index into m pops the element at index i from the list.
• We cannot pop from an empty list (IndexError).
• m.index(x) will return the index of the first occurrence of x in m. Note: This will raise ValueError if x is not in m.

Copyright © 2023–2025 Clayton Cafiero

No generative AI was used in producing this material. This was written the old-fashioned way.