Chapter 6
Collections
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Overview
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
List Literal
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Lists
Due to Python’s dynamic nature, lists may contain values of unrelated types or have
unrelated purpose.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Lists
If you can’t describe a list as a collection of one kind of thing your program design
likely has a problem.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Common List Operations
Table 0.0.1: Common List Operations
Operation
Description
x = [y_1, ..., y_n]
Create a new list with y_1 ... y_n.
x[i]
x[i] = y
Retrieve the value in x associated with
index i.
Set the value in x associated with index i
to y.
x[i:j]
Create a new list with values associated
with indexes i to j (exclusive)
x.append(y)
Append y to the list x.
x.insert(i, y)
Insert y into the list at index i.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Common List Operations
Table 0.0.1: Common List Operations
Operation
del x[i]
Description
Remove the entry in x associated with
index i.
len(x)
Return the number of elements in x.
list(x)
Produces a list from sequence x.
y in x
Returns True if y is in the list x. Returns
False otherwise.
x.sort()
Sort the items in x in place.
x.reverse()
Reverse the items in x in place.
x+ y
Concatenate the lists x and y to form a
new list.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
List Element Access
Like strings, list elements are numbered sequentially starting at zero or using negative
indexes from the end of the list.
0
1
2
3
4
’ Fr ed’
’ Daphne’
’ Vel ma’
’ Shaggy’
’ Scooby’
-5
-4
-3
-2
-1
Using this convention we can access elements of a list much like we do for individual
characters in a string.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
List Element Access
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
List Slicing
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Changing Contents of a List
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Lists are Mutable
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Splitting Strings
One really useful way of generating a list is by splitting a string into substrings. This is
accomplished using the string split method.
By default split uses whitespace to divide the substrings but different separators can
be passed as an argument.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Lists of Lists
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Lists of Lists
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Multi-Dimensional Lists
Accessing individual elements of the matrix uses standard list notation but beware
that the outer list represents the row and the inner list represents the column.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Multi-Dimensional Lists
If we changed the numbers in the matrix to X's and O's we could represent a Tic-TacToe board.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionaries
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionaries
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionaries
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionaries
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionaries
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionary Operations
Table 0.0.1: Common Dictionary Operations
Operation
Description
x = {k_1: y_1, ...,
Create a new dictionary with key value
k_2: y_n]
pairs (k_1, y_1) ... (k_n, y_n).
x[k]
x[k] = y
del x[k]
Retrieve the value in x associated with key
k.
Set the value in x associated with key k to
y.
Remove the entry in x associated with key
k.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Dictionary Operations
Table 0.0.1: Common Dictionary Operations
Operation
Description
len(x)
Return the number of elements in x.
y in x
x.items()
Returns True if the key y in the dictionary
x. Returns False otherwise.
Return an iterable sequence of key value
pairs.
x.keys( )
Return an iterable sequence of keys.
x.values()
Return an iterable sequence of values.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Tuple Literal
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Tuples
Tuples are formed like lists but using parenthesis instead of brackets:
A single element tuple must have a trailing comma:
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Tuple Operations
Table 0.0.1: Common Tuple Operations
Operation
Description
x = (y_1, ..., y_n)
Create a new tuple with y_1 ... y_n.
x[i]
x[i:j]
Retrieve the value in x associated with
index i.
Create a new tuple with values associated
with indexes i to j (exclusive)
len(x)
Return the number of elements in x.
tuple(x)
Produces a tuple from a sequence x.
y in x
x+ y
Returns True if y is in the tuple x. Returns
False otherwise.
Concatenate the lists x and y to form a
new list.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Tuples
Python also has some syntactic shorthand for tuples such that commas outside of a
list or dictionary also define a tuple.
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.
Tuple Unpacking
Copyright © 2014 Dr. James D. Palmer; http://jdpalmer.org/cs1
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.