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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Matching a license plate or product code - Regular Expressions

Questions from my mailbox:

1. Regular expression to accept the following form of license plate numbers. Three letters followed by between 1 and 4 digits.
2. A regular expression to accept the following product codes: Between 1 and three characters (in capitals) followed by between one and three digits.




OK - for the newcomer to regular expressions, let me rephrase those:

1. How do I tell if a character string contains text that's in the right format for a car's number plate which (in the questioner's country) is three letters followed by between one and four digits. The questioner, I note, does NOT state that he wants to check for capital letters.

2. How do I tell if a character string contains text for a product code which consists of between one and three capital(?) letters, followed immediately by between one an three digits.

The answer to pattern matching of this sort is - as correctly identifified by my questioner - a regular expression. In regular expressions, we define a pattern and then ask if the incoming string matches the pattern - here is code (in Python, as I don't know what language my correspondent wants, and I'm feeling like writing some Python today!) that does the trick:

 import re
 
 samples = ["ABC1234", "ABC12", "ABC12345", "BC123", "ABC 14", "Abc123", "123ABC"]
 license_plate = re.compile(r"^[A-Z]{3}\d{1,4}$",re.I)
 product_code = re.compile(r"^[A-Z]{1,3}\d{1,4}$")
 
 for option in samples:
   ml = "No "; mp = "No "
   if license_plate.search(option): ml = "Yes"
   if product_code.search(option): mp = "Yes"
   print ml, mp, option


And here is the sample output:

wizard:mar11 graham$ python regex
Yes Yes ABC1234
Yes Yes ABC12
No No ABC12345
No Yes BC123
No No ABC 14
Yes No Abc123
No No 123ABC
wizard:mar11 graham$


I have made a number of assumptions here - that the product code or license plate number is the complete string, that neither of the formats allow embedded spaces, etc; these are the sort of pedantic issues you need to consider.

Regular Expressions can be daunting at first - but get much easier after explanation and a bit of practise. We cover them on our Python Courses ... and most of our other programming courses too ([list / schedule]). We also offer a special regular expression day - see [here] - for delegates who are familiar with a language, but need that extra bit of training and help with regular expressions. Exceptionally in what we teach, Lua includes a pattern matching scheme that is not based on regular expressions
(written 2011-03-28)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y108 - Python - String Handling
  [324] The backtick operator in Python and Perl - (2005-05-25)
  [463] Splitting the difference - (2005-10-13)
  [496] Python printf - (2005-11-15)
  [560] The fencepost problem - (2006-01-10)
  [773] Breaking bread - (2006-06-22)
  [903] Pieces of Python - (2006-10-23)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [954] Splitting Pythons in Bradford - (2006-11-29)
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [1110] Python - two different splits - (2007-03-15)
  [1195] Regular Express Primer - (2007-05-20)
  [1517] Python - formatting objects - (2008-01-24)
  [1608] Underlining in Perl and Python - the x and * operator in use - (2008-04-12)
  [1876] Python Regular Expressions - (2008-11-08)
  [2284] Strings as collections in Python - (2009-07-12)
  [2406] Pound Sign in Python Program - (2009-09-15)
  [2692] Flexible search and replace in Python - (2010-03-25)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2780] Formatted Printing in Python - (2010-05-25)
  [2814] Python - splitting and joining strings - (2010-06-16)
  [3090] Matching to a string - what if it matches in many possible ways? - (2010-12-17)
  [3349] Formatting output in Python through str.format - (2011-07-07)
  [3468] Python string formatting - the move from % to str.format - (2011-10-08)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [4027] Collections in Python - list tuple dict and string. - (2013-03-04)
  [4152] Why are bus fares so high? - (2013-08-18)
  [4213] Formatting options in Python - (2013-11-16)
  [4307] Identifying and clearing denial of service attacks on your Apache server - (2014-09-27)
  [4360] Python - comparison of old and new string formatters - (2014-12-22)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4595] Python formatting update - including named completions - (2015-12-10)
  [4659] Prining a pound sign from Python AND running from the command line at the same time - (2016-03-03)

Q806 - Regular Expression Cookbook
  [672] Keeping your regular expressions simple - (2006-04-05)
  [1230] Commenting a Perl Regular Expression - (2007-06-12)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1840] Validating Credit Card Numbers - (2008-10-14)
  [2165] Making Regular Expressions easy to read and maintain - (2009-05-10)
  [2563] Efficient debugging of regular expressions - (2010-01-04)
  [2608] Search and replace in Ruby - Ruby Regular Expressions - (2010-01-31)
  [2702] First and last match with Regular Expressions - (2010-04-02)
  [2727] Making a Lua program run more than 10 times faster - (2010-04-16)
  [2804] Regular Expression Myths - (2010-06-13)
  [3788] Getting more than a yes / no answer from a regular expression pattern match - (2012-06-30)


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How do I become a Linux System Administrator?
Some other Articles
Clickjacking - another way to get you to follow a malicious link - Facebook issue
How long is a speech?
Panasonic Lumix TZ20
How do I become a Linux System Administrator?
Matching a license plate or product code - Regular Expressions
Vandalism and riot from the minority - the effect
Images of a Spring Walk
Solution looking for problem
Melksham Campus - any last minute inputs from Melksham businesses?
Should I use Open Source or Commercial software?
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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