Module 2 video notes.docx - Using Python to Access Web...

Using Python to Access Web Date:
Video 11.1
Two: Regular Expressions: Part 1
Chapter 11:
So welcome to Chapter 11. Chapter 11’s kind of a fun chapter because you
don’t really need to now regular expressions. And so, if you just want to skip
ahead, or maybe do the assignment or whatever, but this is kind of fun,
regular expressions are a neat little thing. They are real old concept, they’re
kind of an ancient notation and having to do with the study of languages, not
really exactly computer programming languages, but languages, and
grammars, and what is in a language and what is not in the language, and
regular expression is a form of a language, and meaning it’s a way to say
that a set of strings match or don’t match a regular expression.
 Regular Expressions- In computing, a regular expression, also referred
to as “regex” or “regexp”, provides a concise and flexible means for
matching strings of text, such as particular characters, words, or
patterns of characters. A regular expression is written in a formal
language that can be interpreted by a regular expression processor.
 Understanding Regular Expressions:
o Very powerful and quite cryptic
o Fun once you understand them
o Regular expressions are a language unto themselves
o A language of “marker characters” – programming with
characters
o It is kind of an “old school” language – compact
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Video 11.2 Extracting Date
So, now we’re going to talk about extracting data. Up to now, we’ve just
been playing with the search which gives us back a true or a false depending
on whether it matches or not. But now we’re going to actually pull stuff out.
So, we’re going to start by looking at a different regular expression, a new
regular expression.
 The square bracket is kind of weird and that it is one character.
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 So, that is describing in between the square brackets what we mean by
a single character.
 We can have a range in here.
 Like AEIOU would be vowels.
 Zero through nine is digit.
 So, bracket zero dash nine bracket is a single digit.
 But then, we added a plus to it and that says one or more digits.
 Now if we put a star that zero or more digits which is kind of weird.
 But one or more digits, and now we’re going to use a function called
findall, a function in the regular expression library called findall.
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 So, what we’re saying here is the string we’re looking looking through,
x, and we’re looking for the pattern, one or more digits.
 So the it’s going to look and say, “Oh let me see one or more digits.”
Oh! That looks good like that one let’s keep looking,. That’s good, and
let’s keep looking and that’s good.
 So, it may find zero, it may find one, or it may find more than one.
 So, what it does is it runs all the way through the texts that you’ve
asked it to look for, checking to see when this matches, and it gives us
back a list of the matches.