In this part of my Learn to Program series I finish my coverage of Regular Expressions. We’ll look at Or, Group, Named Groups, More Match Object Functions and then we’ll solve some problems. If you missed the previous Regular Expression tutorials they start here.

All of the code and a transcript of the video follows the video below.

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Code & Transcript

import re

# [ ]   : Match what is in the brackets
# [^ ]  : Match anything not in the brackets
# ( )   : Return surrounded submatch
# .     : Match any 1 character or space
# +     : Match 1 or more of what proceeds
# ?     : Match 0 or 1
# *     : Match 0 or More
# *?    : Lazy match the smallest match
# \b    : Word boundary
# ^     : Beginning of String
# $     : End of String
# \n    : Newline
# \d    : Any 1 number
# \D    : Anything but a number
# \w    : Same as [a-zA-Z0-9_]
# \W    : Same as [^a-zA-Z0-9_]
# \s    : Same as [\f\n\r\t\v]
# \S    : Same as [^\f\n\r\t\v]
# {5}   : Match 5 of what proceeds the curly brackets
# {5,7} : Match values that are between 5 and 7 in length
# ($m)  : Allow ^ on multiline string

# Use a back reference to substitute what is between the
# bold tags and eliminate the bold tags
# re.sub(r"<b>(.*?)</b>", r"\1", randStr)

# Use a look ahead to find all characters of 1 or more
# with a word boundary, but don't return the word
# boundary
# re.findall(r"\w+(?=\b)", randStr)

# Use a look behind to find words starting with a number,
# period and space, but only return the word that follows
# re.findall(r"(?<=\d.\s)\w+", randStr)

# Use a negative look behind to only return numbers without
# a $ in front of them
# re.findall(r"(?<!\$)\d+", randStr)

# ---------- OR CONDITIONAL ----------
# You can use | to define the matches you'll except

randStr = "1. Dog 2. Cat 3. Turtle"

regex = re.compile(r"\d\.\s(Dog|Cat)")

matches = re.findall(regex, randStr)

print(len(matches))

for i in matches:
    print(i)

# ---------- PROBLEM ----------
# Create a regex that will match for 5 digit zip
# codes or zip codes with 5 digits a dash and
# then 4 digits

randStr = "12345 12345-1234 1234 12346-333"

regex = re.compile(r"(\d{5}-\d{4}|\d{5}\s)")

matches = re.findall(regex, randStr)

print(len(matches))

for i in matches:
    print(i)

# ---------- GROUP ----------
# We can use group to retrieve parts of regex
# matches
'''
bd = input("Enter your birthday (mm-dd-yyyy) : ")

bdRegex = re.search(r"(\d{1,2})-(\d{1,2})-(\d{4})", bd)

print("You were born on", bdRegex.group())
print("Birth Month", bdRegex.group(1))
print("Birth Day", bdRegex.group(2))
print("Birth Year", bdRegex.group(3))
'''

# ---------- MATCH OBJECT FUNCTIONS ----------
# There are functions that provide more information
# on your matches

match = re.search(r"\d{2}", "The chicken weighed 13 lbs")

# Print the match
print("Match :", match.group())

# Print the start and ending index of the match
print("Span :", match.span())

# Print starting index of the match
print("Match :", match.start())

# Print the ending index of the match
print("Match :", match.end())

# ---------- NAMED GROUPS ----------
# You can also assign names to matches

randStr = "December 21 1974"

regex = r"^(?P<month>\w+)\s(?P<day>\d+)\s(?P<year>\d+)"

matches = re.search(regex, randStr)

print("Month :", matches.group('month'))
print("Day :", matches.group('day'))
print("Year :", matches.group('year'))

# ---------- PROBLEM ----------
# Find all of the following email addresses

randStr = "d+b@aol.com a_1@yahoo.co.uk A-100@m-b.INTERNATIONAL"

regex = re.compile(r"[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+")

matches = re.findall(regex, randStr)

print(len(matches))

for i in matches:
    print(i)

# ---------- PROBLEM ----------
# Find all of the following phone numbers and then print them

randStr = "14125551212 4125551212 (412)5551212 412 555 1212 412-555-1212 1-412-555-1212"

regex = re.compile(r"((1?)(-| ?)(\()?(\d{3})(\)|-| |\)-|\) )?(\d{3})(-| )?(\d{4}|\d{4}))")

matches = re.findall(regex, randStr)

print(len(matches))

for i in matches:
    print(i[0].lstrip())