Processing Regex Python

1. PROCESSING TEXT
WITH REGEX

2. WHY IS REGEX NECESSARY?
 Question: What does the following script do?
def isPhoneNUmber(text):
if len(text) != 12:
return False
for i in range(0, 3):
if not text[i].isdecimal():
return False
if text[3] != ‘-’:
return False
for i in range(4, 7):
if not text[i].isdecimal():
return False
if text[7] != ‘-’:
return False
for i in range(8, 12):
if not text[i].isdecimal():
return False
return True

3. WHY IS REGEX NECESSARY?
 Question: What about this one?
message = raw_input(“Enter a string”)
for I in range(len(message)):
chunk = message[i: i+12]
if (isPhoneNumber(chunk):
print “Phone number found: “ + chunk
Print “Done”

4. ARE THEY THAT IMPORTANT?
 Regular Expressions as we have previously discussed are dynamic
descriptive patterns designated for searching (pattern recognition).
 Ex.
 Without regular expressions you are hard coding fixed values to
search for
 = vs. like

5. INCORPORATING REGEX IN
PYTHON
 Python once again makes life simpler by having a prebuilt module to
simplify incorporating the code into your scripts.
 Enter the re module
 Code: import re
 There are 2 benefits to using the re module:
1) Predefined Functions: compile(), search(), findall()
2) The RegEx syntax is almost identical to Perl

6. PYTHON’S REGEX CHEAT SHEET

7. COMPILING A REGEX EXPRESSION
 Each iteration that a RegEx expression is used in python must be reread
and interepretted.
 Thus if you were to search through an entire document each line would
have to reinterpret the expression.
 This can cause increased execution times and inefficiency.
 The ‘re’ module has a function that will compile the expression for easy
reusability.
 Code: varName = re.compile(REGEX EXPRESSION)
 Ex. phoneNumRegEx = re.compile(“ddd-ddd-dddd”)

8. THE SEARCH FUNCTION
 The search() function will search a document for the first occurrence of
the pattern.
 It will return a True or False value depending on if there was a match to
the pattern.
 Code: compExpVar.search(TEXT)
 Ex. phNumRegEx = re.compile(“ddd-ddd-dddd”)
mo = phNumRegEx.search(“Here is 444-343-3243”)
print mo
print mo.group()

9. LET’S FIND EVERYTHING
 In addition to the search() function, the ‘re’ module also has a findall()
function.
 findall() will return all of the strings that match the RegEx expression.
 Code: compExpVar.findall(TEXT)
 Ex. phNumRegEx = re.compile(“ddd”)
mo = phNumRegEx.findall(“Here is 444-343-3243”)
print mo