Learn to Program 16

Posted by Derek Banas on Aug 10, 2016 in Web Design | 0 comments

In this video we’ll continue learning about regular expressions. We’ll cover +, *, Greedy Matching, Lazy Matching, \b, String Boundaries ^ and $, (?m), Subexpressions and we’ll solve a bunch of problems.

If you missed the last regular expression video it is here. All of the code and a transcript of the video follows the video below.

If you like videos like this consider donating a $1 on Patreon.

[googleplusone]

Code & Transcript

import re

# Did you find a match
# if re.search("REGEX", yourString)

# Get list of matches
# print("Matches :", len(re.findall("REGEX", yourString)))

# Get a pattern object
# regex = re.compile("REGEX")

# Substitute the match
# yourString = regex.sub("substitution", yourString)

# [ ]   : Match what is in the brackets
# [^ ]  : Match anything not in the brackets
# .     : Match any 1 character or space
# +     : Match 1 or more of what proceeds
# \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

# ---------- Matching Zero or One ----------

randStr = "cat cats"

regex = re.compile("[cat]+s?")

matches = re.findall(regex, randStr)

# Match cat or cats
print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- Matching Zero or More ----------
# * matches zero or more of what proceeds it

randStr = "doctor doctors doctor's"

# Match doctor doctors or doctor's
regex = re.compile("[doctor]+['s]*")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

# You can do the same by setting an interval match
regex = re.compile("[doctor]+['s]{0,2}")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- PROBLEM ----------
# On Windows newlines are some times \n and other times \r\n
# Create a regex that will grab each of the lines in this
# string, print out the number of matches and each line

longStr = '''Just some words
and some more\r
and more
'''

print("Matches :", len(re.findall(r"[\w\s]+[\r]?\n", longStr)))

matches = re.findall("[\w\s]+[\r]?\n", longStr)

for i in matches:
    print(i)

# ---------- Greedy & Lazy Matching ----------

randStr = "<name>Life On Mars</name><name>Freaks and Geeks</name>"

# Let's try to grab everything between <name> tags
# Because * is greedy (It grabs the biggest match possible)
# we can't get what we want, which is each individual tag
# match
regex = re.compile(r"<name>.*</name>")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# We want to grab the smallest match we use *?, +?, or
# {n,}? instead

regex = re.compile(r"<name>.*?</name>")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- Word Boundaries ----------
# We use word boundaries to define where our matches start
# and end

# \b matches the start or end of a word

# If we want ape it will match ape and the beginning of apex
randStr = "ape at the apex"

regex = re.compile(r"ape")

# If we use the word boundary
regex = re.compile(r"\bape\b")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- String Boundaries ----------
# ^ : Matches the beginning of a string if outside of
#     a [ ]
# $ : Matches the end of a string

# Grab everything from the start of the string to @
randStr = "Match everything up to @"

regex = re.compile(r"^.*[^@]")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# Grab everything from @ to the end of the line
randStr = "@ Get this string"

regex = re.compile(r"[^@\s].*$")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# Grab the 1st word of each line using the the multiline
# code which allows for the targeting of each line after
# a line break with ^
randStr = '''Ape is big
Turtle is slow
Cheetah is fast'''

regex = re.compile(r"(?m)^.*?\s")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- Subexpressions ----------
# Subexpressions are parts of a larger expression
# If you want to match for a large block, but
# only want to return part of it. To do that
# surround what you want with ( )

# Get just the number minus the area code
randStr = "My number is 412-555-1212"

regex = re.compile(r"412-(.*)")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- Problem ----------

# Get just the numbers minus the area codes from
# this string
randStr = "412-555-1212 412-555-1213 412-555-1214"

regex = re.compile(r"412-(.{8})")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:
    print(i)

# ---------- Multiple Subexpressions ----------

# You can have multiple subexpressions as well
# Get both numbers that follow 412 separately
randStr = "My number is 412-555-1212"

regex = re.compile(r"412-(.*)-(.*)")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

print(matches[0][0])
print(matches[0][1])

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

import re

# Did you find a match

# if re.search("REGEX", yourString)

# Get list of matches

# print("Matches :", len(re.findall("REGEX", yourString)))

# Get a pattern object

# regex = re.compile("REGEX")

# Substitute the match

# yourString = regex.sub("substitution", yourString)

# [ ] : Match what is in the brackets

# [^ ] : Match anything not in the brackets

# . : Match any 1 character or space

# + : Match 1 or more of what proceeds

# \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

# ---------- Matching Zero or One ----------

randStr = "cat cats"

regex = re.compile("[cat]+s?")

matches = re.findall(regex, randStr)

# Match cat or cats

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- Matching Zero or More ----------

# * matches zero or more of what proceeds it

randStr = "doctor doctors doctor's"

# Match doctor doctors or doctor's

regex = re.compile("[doctor]+['s]*")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

# You can do the same by setting an interval match

regex = re.compile("[doctor]+['s]{0,2}")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- PROBLEM ----------

# On Windows newlines are some times \n and other times \r\n

# Create a regex that will grab each of the lines in this

# string, print out the number of matches and each line

longStr = '''Just some words

and some more\r

and more

'''

print("Matches :", len(re.findall(r"[\w\s]+[\r]?\n", longStr)))

matches = re.findall("[\w\s]+[\r]?\n", longStr)

for i in matches:

print(i)

# ---------- Greedy & Lazy Matching ----------

randStr = "<name>Life On Mars</name><name>Freaks and Geeks</name>"

# Let's try to grab everything between <name> tags

# Because * is greedy (It grabs the biggest match possible)

# we can't get what we want, which is each individual tag

# match

regex = re.compile(r"<name>.*</name>")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# We want to grab the smallest match we use *?, +?, or

# {n,}? instead

regex = re.compile(r"<name>.*?</name>")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- Word Boundaries ----------

# We use word boundaries to define where our matches start

# and end

# \b matches the start or end of a word

# If we want ape it will match ape and the beginning of apex

randStr = "ape at the apex"

regex = re.compile(r"ape")

# If we use the word boundary

regex = re.compile(r"\bape\b")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- String Boundaries ----------

# ^ : Matches the beginning of a string if outside of

# a [ ]

# $ : Matches the end of a string

# Grab everything from the start of the string to @

randStr = "Match everything up to @"

regex = re.compile(r"^.*[^@]")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# Grab everything from @ to the end of the line

randStr = "@ Get this string"

regex = re.compile(r"[^@\s].*$")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# Grab the 1st word of each line using the the multiline

# code which allows for the targeting of each line after

# a line break with ^

randStr = '''Ape is big

Turtle is slow

Cheetah is fast'''

regex = re.compile(r"(?m)^.*?\s")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- Subexpressions ----------

# Subexpressions are parts of a larger expression

# If you want to match for a large block, but

# only want to return part of it. To do that

# surround what you want with ( )

# Get just the number minus the area code

randStr = "My number is 412-555-1212"

regex = re.compile(r"412-(.*)")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- Problem ----------

# Get just the numbers minus the area codes from

# this string

randStr = "412-555-1212 412-555-1213 412-555-1214"

regex = re.compile(r"412-(.{8})")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

for i in matches:

print(i)

# ---------- Multiple Subexpressions ----------

# You can have multiple subexpressions as well

# Get both numbers that follow 412 separately

randStr = "My number is 412-555-1212"

regex = re.compile(r"412-(.*)-(.*)")

matches = re.findall(regex, randStr)

print("Matches :", len(matches))

print(matches[0][0])

print(matches[0][1])

	Facebook
	YouTube
	Twitter
	LinkedIn

Learn to Program 16

Leave a Reply Cancel reply