Chapter 11: Regex

Question 1

Code that works when the input data is in a particular format but is prone to breakage if there is some deviation from the correct format. Aka easily broken.

Answer 1

brittle code

Question 2

regex + and * characters expand outward to match the LARGEST possible string

Answer 2

greedy matching

Question 3

A command available in most Unix systems that searches through text files looking for lines that match regular expressions.

Answer 3

grep
General Regular Expression Parser

Question 4

A language for expressing more complex search strings. May contain special characters that indicate that a search only matches at the beginning or end of a line or many other similar capabilities.

Answer 4

regular expression
(regex)

Question 5

A special character that matches any character. In regular expressions it’s the period.

Answer 5

wild card

Question 6

regular expression module

Answer 6

re
import re

Question 7

regex method that finds a specified regular expression in text, returns match object

Answer 7

re.search(regex, search string)

Question 8

regex that matches beginning of line

Answer 8

’^’
re.search(‘^From:’, line)

Question 9

regex that matches any character (a wildcard)

Answer 9

. (period/full stop)

re.search(‘F..m’, line) = From, Flam, F#om, etc.

Question 10

regex that applies to the immediately preceding character(s) and indicates to match zero or more times.

Answer 10

*

Question 11

regex that applies to the immediately preceding character(s) and indicates to match one or more times.

Answer 11

+

Question 12

regex method that returns a list of substring(s) that matches a regular expression

Answer 12

re.findall(substring, search string)
For loop: [‘substring1’][‘substring2’]

Question 13

regex that matches non-whitespace character

Answer 13

\S

Question 14

regex format to accept specific characters

Answer 14

’[]’
Set notation

re.findall(‘[a-zA-Z0-9]’)

Question 15

regex format to match an actual period

Answer 15

[.] or \.

Question 16

When added to a regular expression, they are ignored for the purpose of matching, but allow you to extract a particular subset of the matched string rather than the whole string when using findall().

Answer 16

()

re.findall(‘substring(part I want)’, string)

Question 17

technique to insert regex as literal character

Answer 17

backslash
\$ = ‘$’

Question 18

regex that anchors to end of line

Answer 18

$

Question 19

regex that matches a whitespace character

Answer 19

\s

Question 20

regex that applies to the immediately preceding character(s) and indicates to match zero or more times in “non-greedy mode”.

Answer 20

*?

Question 21

regex that applies to the immediately preceding character(s) and indicates to match one or more times in “non-greedy mode”.

Answer 21

+?

Question 22

regex that applies to the immediately preceding character(s) and indicates to match zero or one time.

Answer 22

?

Question 23

regex that applies to the immediately preceding regular expression and indicates to match zero or one time in “non-greedy mode”.

Answer 23

??

Question 24

regex that matches a single character as long as that character is in the specified set. In this example, it would match “a”, “e”, “i”, “o”, “u”, or “-“ but no other characters.

Answer 24

[aeiou-] or [-aeiou]

Question 25

You can specify ranges of characters using the minus sign. This example is a single character that must be a lowercase letter or a digit.

Answer 25

[a-z0-9]

Question 26

When the first character in the set notation is a caret, it inverts the logic. This example matches a single character that is anything other than an uppercase or lowercase letter.

Answer 26

[^A-Za-z]

Question 27

regex that asserts where a word begins or ends. This means that r’\bat\b’ matches ‘at’, ‘at.’, ‘(at)’, and ‘as at ay’ but not ‘attempt’ or ‘atlas’.

Answer 27

\b

Question 28

regex that asserts where a word does NOT begin or end. This means that r’at\B’ matches ‘athens’, ‘atom’, ‘attorney’, but not ‘at’, ‘at.’, or ‘at!’.

Answer 28

\B

Question 29

regex that matches any decimal digit;
equivalent to the set [0-9].

Answer 29

\d

Question 30

regex that matches any non-digit character;
equivalent to the set [^0-9].

Answer 30

\D

Question 31

In Unix/Linux, command-line program similar to the search() function

Answer 31

Generalized Regular Expression Parser
(grep)

$ grep ‘^From:’ mbox.short.txt

Question 32

Unix linux regex for non-blank character

Answer 32

[^ ]

Question 33

regex + and * characters expand outward to match the SMALLEST possible string

Answer 33

non-greedy matching

Question 34

Specifies that exactly m copies of the
previous regular expression should be matched; fewer matches cause the entire regular expression not to match

Answer 34

{m}

Question 35

Causes the resulting regular expression to greedily match from m to n repetitions of the preceding regular expression.

Answer 35

{m,n}

Question 36

Causes the resulting regular expression to non-greedily match from m to n repetitions of the preceding regular expression

Answer 36

{m,n}?

Question 37

Creates a regular expression that will match either A or B.
This operation is never greedy

Answer 37

|

cat|dog = cat or dog

Question 38

Matches the contents of the group of the same number. Groups are numbered starting from 1.
For example, (.+) \1 matches ‘the the’ or ‘55 55’, but not ‘thethe’ (note the space after the group).

(abc)\1matches abcabc. In which,(abc)is a capturing group, and \1is a backreference that matches the same text as captured by the capturing group, so,\1 matches abc too.

Answer 38

\number