How to check subsequent elements of string in python using iterators?

Question

I have a sentence that I want to parse to check for some conditions:

a) If there is a period and it is followed by a whitespace followed by a lowercase letter

b) If there is a period internal to a sequence of letters with no adjacent whitespace (ie www.abc.com)

c) If there is a period followed by a whitespace followed by an uppercase letter and preceded by a short list of titles (ie Mr., Dr. Mrs.)

Currently I am iterating through the string (line) and using the next() function to see whether the next character is a space or lowercase, etc. And then I just loop through the line. But how would I check to see what the next, next character would be? And how would I find the previous ones?

line = "This is line.1 www.abc.com. Mr."

t = iter(line)
b = next(t)

for i in line[:len(line)-1]:
    a = next(t)
    if i == "." and (a.isdigit()): #for example, this checks to see if the     value after the period is a number
         print("True")

Any help would be appreciated. Thank you.

Answer 1

Regular expressions is what you want.

Since your going to check for a pattern in a string, you can make use of the python's builtin support for regular expressions through re library.

Example:

#To check if there is a period internal to a sequence of letters with no adjacent whitespace 
import re
str = 'www.google.com'
pattern = '.*\..*'
obj = re.compile(pattern)
if obj.search(str):
    print "Pattern matched"

Similarly generate patterns for the conditions you want to check in your string.

#If there is a period and it is followed by a whitespace followed by a lowercase letter
regex = '.*\. [a-z].*'

You can generate and test your regular expressions online using this simple tool

Read more extensively about re library here

Answer 2

You can use multiple next operations to get more data

line = "This is line.1 www.abc.com. Mr."

t = iter(line)
b = next(t)

for i in line[:len(line)-1]:
    a = next(t)
    c = next(t)
    if i == "." and (a.isdigit()): #for example, this checks to see if the     value after the period is a number
         print("True")

You can get previous ones by saving your iterations to a temporary list