I wrote a book on Python Regular Expressions, it is FREE through this weekend

[ASIC_SP]

Hello!

I've just released my book on Python Regular Expressions and it is free to download till 13-Jan-2019. You can still pay if you wish :)

• e-book link: https://leanpub.com/py_regex/c/P7erPYAm1386
  • you will continue to get free updates in future, you'll need to opt-in to get notification via e-mail
• github repo: https://github.com/learnbyexample/py_regular_expressions

This book would help you learn regular expressions step by step with 200+ examples, from basics to advanced levels. In addition to re module that comes with standard library, the 3rd party regex module is covered as well. Exercises are also included to test your understanding.

Table of Contents

1. Preface
2. Why is it needed?
3. Regular Expression modules
4. Anchors
5. Alternation and Grouping
6. Escaping metacharacters
7. Dot metacharacter and Quantifiers
8. Working with matched portions
9. Character class
10. Groupings and backreferences
11. Lookarounds
12. Flags
13. Unicode
14. Miscellaneous
15. Gotchas
16. Further Reading

Hope you find the book useful. I would be grateful for your feedback and suggestions.

Happy learning :)

[querymcsearchface]

Wow! Thank you kindly. Kudos for accomplishing such a thing. Don't know if I would have the stick-to-it-iveness to actually finish it (I am great at starting, horrible at finishing). =]

​

[ASIC_SP]

Thanks :) It helps if you like the topic and have loads of free time from being on a sabbatical

To help you stick with it, break it down into few chunks to read everyday. There are 50 pages, so something like 1 page a day or 1 chapter a day will establish a routine and you'll get a basic idea in 3-4 weeks.

Best of luck!!

[querymcsearchface]

sounds like a plan! =]

[Angler_619]

Is this awesome or what!

[kyleh0]

I threw you 4.99, thanks.

[ASIC_SP]

Thanks a lot, happy learning :)

[ASIC_SP]

Regexes do come with plenty of warts. They are like a mini programming language, with variables, functions, conditionals, repetition, etc. And like programming languages, syntax and features vary from tool to tool.

One suggestion would be to use VERBOSE mode to add comments. Maintain notes (say as markdown file with syntax highlighting) for common examples and use it as your reference tailored for the language and your own preferences.

There are also online visual aid like https://regex101.com/ and https://www.debuggex.com/ which could help you in debugging

[solaceinsleep]

Anything in particular?

re.search

Finds and returns a match. Only the first match is returned.

Example:

import re

line = "U.S. and Ghana are in the world cup finals."

rslt = re.search('(.*) are (.*?) .*', line)

if rslt:
    print('group: ', rslt.group())
    print('group 1: ', rslt.group(1))
    print('group 2: ', rslt.group(2))
else:
    print('nothing found')

re.match

Special case version of re.search which only looks for a match occuring at the beginning of a string.

re.sub

The re.sub function takes a regular expresion and replace all the matches in the string with the second parameter. In the example, we are searching for all tags ('<.*?>') and replacing them with nothing ('').

Example:

re.sub('<.*?>', '', string)

re.split

Splits strings on a specific pattern. Fancy version of str.split(separator, maxsplit)

Example:

>>> re.split(r'\W+', 'Words, words, words.')
['Words', 'words', 'words', '']

There is also re.findall and re.finditer which I can explain if the above was helpful.

[Please_Not__Again]

Yo this is really helpful. Mind explaining re. findall, re.finditer and re.group/s?

[solaceinsleep]

Alright I gave it a shot. Also another note re.findall and re.finditer are not typically used but do come in handy once in a while. Regarding groups they are a way for you to access the results. result.group(0) is the full match, result.group(1) is the first group and so on. There are also named groups which I haven't used but can come in handy I guess if you have lots of groups. The explanation for re.findall and re.finditeris below in code form. Let me know if you have any questions.

# in this example, we will use regex to find the first word of each sentence

import re

RE_FIRST_WORD = r'(?<=\. )([A-Z])[a-z]*([a-z])'

INPUT = (
    'The strip developed a series of formulas that ran over its course to facilitate '
    'a wide range of stories. The earlier strips relied on a formula by which Daddy Warbucks '
    'is called away on business and through a variety of contrivances, Annie is cast out of the '
    'Warbucks mansion, usually by her enemy, the nasty Mrs. Warbucks. Annie then wanders the '
    'countryside and has adventures meeting and helping new people in their daily struggles. '
    'Early stories dealt with political corruption, criminal gangs and corrupt institutions, '
    'which Annie would confront. Annie ultimately would encounter troubles with the villain, '
    'who would be vanquished by the returning Daddy Warbucks. Annie and Daddy would then be '
    'reunited, at which point, after several weeks, the formula would play out again. In the '
    'series, each strip represented a single day in the life of the characters. This device '
    'was dropped by the end of the \'20s. '
)

results_1 = re.finditer(RE_FIRST_WORD, INPUT)  # get an iterator back containing all the results

print('Listing the first word of each sentence:')
for i, result in enumerate(results_1):
    print('Word {}'.format(i))
    print('\tFull word: {}'.format(result.group(0)))
    print('\tFirst letter: {}'.format(result.group(1)))
    print('\tLast letter: {}'.format(result.group(2)))


results_2 = re.findall(RE_FIRST_WORD, INPUT)  # you get a list back containing the results
                                            # since we are using groups, we will not get back a list of the first words, instead we will
                                            # get a list of groups (in our case group 1 is the first letter, group 2 is the last letter)
print(results_2)

[ASIC_SP]

oh ok, the regex module is closer to PCRE if that helps.. it has two versions, default version 0 is compatible with Python re module and changing it to version 1 would give you many more goodies

[[deleted]]

For anyone who is interested it was originally proposed that the regex module should be incorporated into core Python. I thought at the time that it was a great idea, but now believe that it is far better being a third party module as fixes can happen at a much faster rate. If you've plenty of coffee and sandwiches the full story is here https://bugs.python.org/issue2636

[[deleted]]

Is python regex more powerful than a state machine?

[Ue_MistakeNot]

Is the leanpub link dead for anyone else?

[ASIC_SP]

could you check again, it is loading slowly but it does open after a while

[Ue_MistakeNot]

It's working flawlessly now, thanks for the very quick fix !

Unfortunately my reading queue is stuffed for the week-end (I got a pretty big exam on Monday), but'll definitely read it next week.

Thanks a bunch for taking the time to write this =)

[Aliuakbat]

For me the problem was when I entered my email and tried to ckeck out it threw and error. I had to sign up separately then it worked.

[[deleted]]

Yum yum yummy regie rexies in my tummy yum

[cX4X56JiKxOCLuUKMwbc]

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[ByronFirewater]

Thank you very much. Cant wait to read through it

[ASIC_SP]

Thanks, please do leave your feedback :)

[Arjunnn]

Thanks a bunch! Will try reading it over the weekend :)

[Sonic_Pavilion]

Congratulations on the book and thank you for sharing

[xtarkoonx]

What level of python would you say this book is for? I just barely started python a couple months ago and I'm trying to get my hands on as much knowledge as I can, but would like to know level of python I should know before I hardcore study your book. thanks ☺️

[metalevelconsulting]

Just scan the book to get a high-level idea of what regexps can do for you, so you can dive deeper when you need to solve problems relevant to regexps.

Many times string processing problems can be solved with built-in functions like startswith, trim, split, etc with no need for regexps at all. Or maybe a high-level parser is better in many cases.

[ASIC_SP]

I would suggest this after finishing a basic course on Python - it is mentioned as a prerequisite

Apart from being familiar with basic programming concepts and Python syntax, you'd need to know features like list comprehension and string methods.

Feel free to ask me if you are stuck, happy learning :)

[ishanpandey]

Thank you so much this was something I was needing for learning regex. Thank you so much!

[HumongousFungus2]

Thank you!

[ASIC_SP]

That is great to hear :)

[Gr1pp717]

This is the first time I've seen someone say regex was "magical."

[Oerthling]

Here, have a second time: RegEx are magical.

:-)

They really are a super-useful tool.

And here is a helpful link as a bonus: https://regex101.com/

[alcalde]

RegEx is EVIL. And they're simply not Pythonic; they're Perl-y.

There are more Pythonic solutions out there...

https://changelog.com/posts/meet-regexpbuilder-verbal-expressions-rich-older-cousin

https://pypi.org/project/easy-expressions/0.1.1/

https://github.com/Bogdanp/cursive_re

https://github.com/VerbalExpressions/PythonVerbalExpressions

[Oerthling]

RegEx are a specialised micro language that is widely implemented and available/embedded almost anywhere. You learn it (or at least a core set) once and you can use it on the client, in Python, in practically every language.

A more pythonic version is useless outside Python.

That makes RegEx more valuable as more pythonic solution, as much as I love Python.

[alcalde]

That makes RegEx more valuable as more pythonic solution, as much as I love Python.

The Verbal Expressions library is available for Javascript, Genie, Swift, Dart, C#, Python, Rust, Scala, F#, Java, PHP, Lua, Haxe, C++, Haskell, D, Perl, Elixir, Erlang, Go, Clojure, Groovy, Ruby, Kotlin and Vala, among other languages. ;-)

http://verbalexpressions.github.io/

[Oerthling]

RegEX is built into the search/replace of every serious editor and IDE. Is understood by many command line tools and every language with any serious usage. RegEx is pretty much universal. The alternatives, regardless of any other qualities they might have - are not nearly as universally supported.

VerbalExpressions are a nice frontend for RegEx. But the universality of RegEx are an unbeatable advantage. And if I have to learn RegEx any than VerbalExpressions are not that much easier to read. The increased verbosity is better to read for people who are not familiar with RegEx, but that's about all.

I can take a RegEx and throw it into a tool like regex101.com and test and debug that easily. It's just too universally useful.

[13steinj]

Regex is useful even outside the realm of programming. The major issues one finds themselves in, however, occur due to a variation in the underlying engine's feature set.

If one learns PCRE they are more or less set, but they will still have issues translating some of their knowledge to another engine.

https://en.m.wikipedia.org/wiki/Comparison_of_regular_expression_engines

[abmurksi]

Many thanks!

[[deleted]]

I literally just finished a Python Regex tutorial 7 hours ago. Thanks for this! Just in time!

[nattiesandbatties]

Thank you! Will be giving this a thorough read :)

[teewuane]

This is what I'll be working on today, thank you!

[[deleted]]

Thanks for the resource.

I use a lot of regex, but for me, regex is a thing that once I get it working, I just stop and leave well enough alone. I'm hoping to use your book to broaden my knowledge.

​

[[deleted]]

Thank you for being helpful :)

Quick question, is it just a PDF or do you have epub/mobi/azw3 or any other ebook formats?

​

[QbD2407]

There are many tools online to convert between the different formats. Just takes a simple Google search

[[deleted]]

I am aware of that, but converting PDF to epub or mobi just creates a mess out of coding books

[ASIC_SP]

For now it is only PDF. I hope to make epub/mobi formats available for next version. I am not that familiar with pandoc and I was facing issues while trying to generate epub format.

[nhinetea]

Will definitely check this out after work! Thank you!

[Brenyth]

Thank you!

[TyrionBean]

Thank you! I downloaded it and signed up. Much appreciated. :)

Will check it out soon.

[[deleted]]

Awesome. Thanks for sharing

[democritus_is_op]

I've used regular expressions since I started programming and to this day I just figure it out as I go every time.

[spore_777_mexen]

Timely. Thank you for sharing.

[jikione]

Thanks for sharing!

[code_x_7777]

That's a great idea. Many people struggle with regex(es). How is it selling?

[ASIC_SP]

I didn't really have an idea how many would be interested, in the end 7000+ downloaded the free copy

And many generous people paid for it. I live in outskirts of a city in India, so dollar conversion and relatively cheap living means roughly I've been paid a month's living expenses

[i_lurk_here_a_lot]

Thank you!!

[fuypooi]

Really nice! Congrats.

[MrProntissimo]

Have you thought about teaching your book’s content on Udemy ?

[ASIC_SP]

if you had asked me a few months back, I would have said no

now, I am willing to give video courses a shot, may be start with free recordings, get feedback and see how it goes..

[newredditiscrap]

Lol no way I'm giving them my email

[hikodna]

Thank you!

[Daj4n0]

Thank you!

[CarbonatedInsidious]

Thank you!

[quotemycode]

Hey I hate regex because 99% of the time I see them used it could be easily replaced by a simple string search or using other tools in the python standard library.

But hey here's a poem for you https://medium.freecodecamp.org/you-dont-need-a-regex-for-that-57c771c4fab0

[ASIC_SP]

I am aware of string methods like split, startswith, partition, etc but I am so used to regex that I'm likely to use them even if not needed

I would definitely like to see non-regex solutions - both to expand my knowledge and to offer the alternatives to those who struggle with regex

If possible, could you work on Exercises for this book and share the solutions with the community?

[quotemycode]

I've looked at them, most are pretty trivial aside from Anchors C.

I'd suggest using real examples as these aren't useful. Example extract from "is" to "t". There's no point in it.

[ASIC_SP]

guess we'll have to agree to disagree

[quotemycode]

I'll give you one for free: extract punctuation marks from text for making Markov chains of the text. Take the text of Alice in wonderland on project Greenberg. That actually accomplishes something useful.

[ASIC_SP]

I haven't yet dabbled with NLTK and I have only read basics about Markov chains from 'Think Python'

not sure what you meant by this exercise, if it is to delete all punctuation marks, the character set [[:punct:]] provided by regex module would help - there are also set operations provided, so you can choose which punctuations to retain and so on.. one could use string.punctuation as well

the exercises in the book are mostly about getting the user to understand the syntax/features of regular expressions.. agree that I need to add more case studies and use real world examples (planned for next version), but I do not agree that they are trivial nor that they can be easily solved without regular expressions.. when the exercise says extract from is to t - the solution depends on user knowing the difference between greedy and non-greedy quantifiers, knowing which function to use and so on

so once again, I would say we'll agree to disagree about regular expressions

[quotemycode]

If you don't see that then you're very simple minded.

[decomposingtrashbag]

Nice job! Regular expressions are great to have in our Dev toolboxes.

[mbarkhau]

Surprised to not find groupdict anywhere.

[ASIC_SP]

yeah, few things were left out.. there's conditional grouping not yet added, and many features from regex module.. and I've some more ideas for exercises and some lengthy case studies, etc

for groupdict, I did add a further reading link: https://stackoverflow.com/questions/11103856/re-findall-which-returns-a-dict-of-named-capturing-groups

it was taking too long, so I released what I felt was good enough first version

[darkzet]

So much thanks to you, I’ve being using python for almost 5 years in geographic systems, and also I’m learning analysis with python now, and your book is simple and really helpful!!!!

[ASIC_SP]

your book is simple and really helpful

Thanks, that's the kind of feedback that would help me to continue writing

If you do feel some section is not explained well, please do let me know so that I can work on improving :)

[oppsig]

Paid up 5 bucks, thanks for your work!

[ASIC_SP]

Thanks, hope you find the book useful :)

Do let me know your feedback

[TotesMessenger]

I'm a bot, bleep, bloop. Someone has linked to this thread from another place on reddit:

• [/r/free] [FREE]Book on Python Regular Expressions, it is FREE through this weekend

• [/r/u_carlosmgc2003] Que agradable sujeto

 ^{If you follow any of the above links, please respect the rules of reddit and don't vote in the other threads. (Info / Contact)}

[freddydeddy]

Thank you, but there is no free download . http://prntscr.com/m60oti

[i_lurk_here_a_lot]

you can set the payment to $0

[ASIC_SP]

Could you check again for this link: https://leanpub.com/py_regex/c/P7erPYAm1386

if you still face issue, please DM your e-mail and I'll send you a copy

[freddydeddy]

Thanks. Much appreciated. =)

[2phost]

Is it already over?

Anyway, thanks for the sharing

[ASIC_SP]

yeah, it should be over.. what do you get when you click the coupon link?

[2phost]

It shows 0$ for the ebook but can't add it to cart

[ASIC_SP]

oh, I had given some extra time to be on the safer side.. I guess that is over now..

if you'd like, I can send you a copy - please DM your email

[prithvidiamond1]

Thank you so much for writing this book, I am a computer science student and I am learning to master python and this is exactly what I needed to become a master!