Understanding Python regex, Agarwal S.

Understanding Python regex, Agarwal S.

   Scripting and automation tasks often need to extract particular portions of text from input data or modify them from one format to another. This book will help you understand Regular Expressions, a mini-programming language for all sorts of text processing needs. This book heavily leans on examples to present features of regular expressions one by one. It is recommended that you manually type each example and experiment with them. Understanding both the nature of input strings and the output produced is essential. As an analogy, consider learning to drive a car — no matter how much you read about them or listen to explanations, you’d need practical experience to become proficient.




Word anchors.
The third type of restriction is word anchors. Alphabets (irrespective of case), digits and the underscore character qualify as word characters. You might wonder why there are digits and underscores as well, why not just alphabets? This comes from variable and function naming conventions — typically alphabets, digits and underscores are allowed. So, the definition is more oriented to programming languages than natural ones.

The escape sequence \b denotes a word boundary. This works for both the start and end of word anchoring. Start of word means either the character prior to the word is a non-word character or there is no character (start of string). Similarly, end of word means the character after the word is a non-word character or no character (end of string). This implies that you cannot have word boundary \b without a word character.

Contents.
Preface.
Prerequisites.
Conventions.
Acknowledgements. 
Feedback and Errata.
Author info.
License.
Book version. 
Why is it needed?.
How this book is organized. 
re introduction.
re module documentation.
re.search().
re.search() in conditional expressions. 
re.sub(). 
Compiling regular expressions.
bytes.
re(gex)? playground.
Cheatsheet and Summary. 
Exercises.
Anchors.
String anchors. 
re.fullmatch(). 
Line anchors. 
Word anchors. 
Cheatsheet and Summary. 
Exercises.
Alternation and Grouping.
Alternation.
Grouping. 
Precedence rules. 
Cheatsheet and Summary. 
Exercises.
Escaping metacharacters.
Escaping with backslash.
re.escape().
Escape sequences. 
Cheatsheet and Summary. 
Exercises.
Dot metacharacter and Quantifiers.
Dot metacharacter.
re.split(). 
Greedy quantifiers.
Conditional AND.
What does greedy mean?. 
Non-greedy quantifiers. 
Possessive quantifiers. 
Catastrophic Backtracking.
Cheatsheet and Summary. 
Exercises.
Interlude: Tools for debugging and visualization.
regex101. 
debuggex. 
re(gex)? playground.
re(gex)? exercises. 
regexcrossword. 
Summary.
Working with matched portions.
re.Match object.
Assignment expressions. 
Using functions in the replacement section. 
Using dict in the replacement section.
re.findall(). 
re.finditer().
re.split() with capture groups. 
re.subn().
Cheatsheet and Summary. 
Exercises.
Character class.
Custom character sets.
Range of characters.
Negating character sets.
Matching metacharacters literally.
Escape sequence sets. 
Numeric ranges. 
Cheatsheet and Summary. 
Exercises.
Groupings and backreferences.
Backreference.
Non-capturing groups. 
Named capture groups. 
Atomic grouping.
Conditional groups. 
Match.expand(). 
Cheatsheet and Summary. 
Exercises.
Interlude: Common tasks.
CommonRegex.
Summary.
Lookarounds.
Conditional expressions.
Negative lookarounds. 
Positive lookarounds. 
Capture groups inside positive lookarounds. 
Conditional AND with lookarounds. 
Variable length lookbehind. 
Negated groups. 
Cheatsheet and Summary. 
Exercises.
Flags.
re.IGNORECASE.
re.DOTALL.
re.MULTILINE. 
re.VERBOSE. 
Inline comments.
Inline flags. 
Cheatsheet and Summary. 
Exercises.
Unicode.
re.ASCII. 
Codepoints and Unicode escapes. 
\N escape sequence. 
Cheatsheet and Summary. 
Exercises.
regex module 104
Subexpression calls.
Set start of matching portion with \K.
Variable length lookbehind. 
\G anchor.
Recursive matching. 
Named character sets. 
Set operations. 
Unicode character sets. 
Skipping matches. 
\m and \M word anchors. 
Overlapped matches. 
regex.REVERSE flag. 
\X vs dot metacharacter.
Cheatsheet and Summary. 
Exercises.
Gotchas.
Escape sequences. 
Line anchors with \n as the last character. 
Zero-length matches.
Capture group with quantifiers. 
Converting re to regex module.
Optional arguments syntax.
Summary.
Further Reading.



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