Reference guide: Python concepts from module 3; Terms and definitions from Course 7, Module 3

Built-in functions

The following built-in functions are commonly used in Python.

str()

Converts the input object to a string

str(10)

Converts the integer 10 to the string "10"

len()

Returns the number of elements in an object

print(len("security"))

Returns and displays 8, the number of characters in the string "security"

String methods

The following methods can be applied to strings in Python. 

.upper()

Returns a copy of the string in all uppercase letters

print("Security".upper())

Returns and displays a copy of the string "Security" as "SECURITY"

.lower()

Returns a copy of the string in all lowercase letters

print("Security".lower())

Returns and displays a copy of the string "Security" as "security"

.index()

Finds the first occurrence of the input in a string and returns its location

print("Security".index("c"))

Finds the first occurrence of the character "c" in the string "Security" and returns and displays its index of 2

List methods

The following methods can be applied to lists in Python. 

.insert()

Adds an element in a specific position inside the list

username_list = ["elarson", "fgarcia", "tshah"]

username_list.insert(2,"wjaffrey")

Adds the element "wjaffrey" at index 2 to the username_list; the list becomes ["elarson", "fgarcia", "wjaffrey", "tshah"]

.remove()

Removes the first occurrence of a specific element inside a list

username_list = ["elarson", "bmoreno", "wjaffrey", "tshah"]

username_list.remove("elarson")

Removes the element "elarson" from the username_list; the list becomes ["fgarcia", "wjaffrey", "tshah"]

.append()

Adds input to the end of a list

username_list = ["bmoreno", "wjaffrey", "tshah"]

username_list.append("btang")

Adds the element "btang" to the end of the username_list; the list becomes ["fgarcia", "wjaffrey", "tshah", "btang"]

.index()

Finds the first occurrence of an element in a list and returns its index

username_list = ["bmoreno", "wjaffrey", "tshah", "btang"]

print(username_list.index("tshah"))

Finds the first occurrence of the element "tshah" in the username_list and returns and displays its index of 2

Additional syntax for working with strings and lists

The following syntax is useful when working with strings and lists. 

+ (concatenation)

Combines two strings or lists together

device_id = "IT"+"nwp12"

Combines the string "IT" with the string "nwp12" and assigns the combined string of "ITnwp12" to the variable device_id

users = ["elarson", "bmoreno"] + ["tshah", "btang"]

Combines the list ["elarson", "bmoreno"] with the list ["tshah", "btang"] and assigns the combined list of ["elarson", "bmoreno", "tshah", "btang"] to the variable users

[] (bracket notation)

Uses indices to extract parts of a string or list 

print("h32rb17"[0])

Extracts the character at index 0, which is ("h"), from the string "h32rb17"

print("h32rb17"[0:3])

Extracts the slice [0:3], which is ("h32"), from the string "h32rb17"; the first index in the slice (0) is included in the slice but the second index in the slice (3) is excluded

username_list = ["elarson", "fgarcia", "tshah"]

print(username_list[2])

Extracts the element at index 2, which is ("tshah"), from the username_list

Regular expressions

The following re module function and regular expression symbols are useful when searching for patterns in strings. 

re.findall()

Returns a list of matches to a regular expression

import re

re.findall("a53", "a53-32c .E")

Returns a list of matches to the regular expression pattern "a53" in the string "a53-32c .E"; returns the list ["a53"]

\w

Matches with any alphanumeric character; also matches with the underscore (_)

import re

re.findall("\w", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\w" in the string "a53-32c .E"; matches to any alphanumeric character and returns the list ["a", "5", "3", "3", "2", "c", "E"]

.

Matches to all characters, including symbols

import re

re.findall(".", "a53-32c .E")

Returns a list of matches to the regular expression pattern "." in the string "a53-32c .E"; matches to all characters and returns the list ["a", "5", "3", "-", "3", "2", "c", " ", ".", "E"]

\d

Matches to all single digits

import re

re.findall("\d", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\d" in the string "a53-32c .E"; matches to all single digits and returns the list ["5", "3", "3", "2"]

\s

Matches to all single spaces

import re

re.findall("\d", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\s" in the string "a53-32c .E"; matches to all single spaces and returns the list [" "]

\.

Matches to the period character

import re

re.findall("\.", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\." in the string "a53-32c .E"; matches to all instances of the period character and returns the list ["."]

+

Represents one or more occurrences of a specific character

import re

re.findall("\w+", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\w+" in the string "a53-32c .E"; matches to one or more occurrences of any alphanumeric character and returns the list ["a53", "32c", "E"]

*

Represents, zero, one or more occurrences of a specific character

import re

re.findall("\w*", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\w*" in the string "a53-32c .E"; matches to one or more occurrences of any alphanumeric character and returns the list ["a53", " ", "32c", " ", " ", "E"]

{ }

Represents a specified number of occurrences of a specific character; the number is specified within the curly brackets

import re

re.findall("\w{3}", "a53-32c .E")

Returns a list of matches to the regular expression pattern "\w{3}" in the string "a53-32c .E"; matches to exactly three occurrences of any alphanumeric character and returns the list ["a53","32c"]

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Glossary terms from module 3

Algorithm: A set of rules that solve a problem

Bracket notation: The indices placed in square brackets 

Debugging: The practice of identifying and fixing errors in code

Immutable: An object that cannot be changed after it is created and assigned a value

Index: A number assigned to every element in a sequence that indicates its position

List concatenation: The concept of combining two lists into one by placing the elements of the second list directly after the elements of the first list

List data: Data structure that consists of a collection of data in sequential form

Method: A function that belongs to a specific data type

Regular expression (regex): A sequence of characters that forms a pattern

String concatenation: The process of joining two strings together

String data: Data consisting of an ordered sequence of characters

Substring: A continuous sequence of characters within a string