Programming Python

Tasks studies - laboratory

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Scripting Language Lab6

Regular Expressions

Regular expressions are a powerful tool for manipulating strings.
They are available as libraries in most modern programming languages, including Python.
They are useful for two main tasks:

• Checking if a string matches a pattern (e.g., verifying an email format).
• Performing substitutions within a string (e.g., replacing American spelling with British spelling).

In Python, regular expressions are available via the re module, which is part of the standard library.
Once a regular expression is defined, you can use the re.match function to check if it matches the beginning of a string.
If it does, the function returns a match object; otherwise, it returns None.

Other pattern matching functions include re.search and re.findall:

• re.search finds a pattern match anywhere in the string.
• re.findall returns a list of all substrings that match the pattern.

import re

pattern = r"spam"

if re.search(pattern, "ssspamspamspamsp"):
    print(re.search(pattern, "ssspamspamspamsp").span().__getitem__(1))
else:
    print("No match")

The search function returns an object with several methods providing details about the match:

• group() returns the matched string.
• start() and end() return the start and end positions of the first match.
• span() returns the start and end positions as a tuple.

import re

pattern = r"pam"

match = re.search(pattern, "eggspamsausage")
if match:
   print(match.group())
   print(match.start())
   print(match.end())
   print(match.span())

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Search and Replace

One of the most important methods using regular expressions is sub:

re.sub(pattern, repl, string, max=0)

This method replaces all occurrences of pattern in string with repl.
By default, all occurrences are replaced unless max is specified.
The method returns the modified string.

import re

str = "My name is David. Hi David."
pattern = r"David"
newstr = re.sub(pattern, "Amy", str)
print(newstr)

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Metacharacters

The first metacharacter is . (dot), which matches any character except a newline.

import re

pattern = r"gr.y"

if re.match(pattern, "grey"):
   print("Match 1")

if re.match(pattern, "gray"):
   print("Match 2")

if re.match(pattern, "blue"):
   print("Match 3")

Next, we have ^ and $:

• ^ matches the beginning of a string.
• $ matches the end of a string.

import re

pattern = r"^gr.y$"

if re.match(pattern, "grey"):
   print("Match 1")

if re.match(pattern, "gray"):
   print("Match 2")

if re.match(pattern, "stingray"):
   print("Match 3")

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Character Classes

Character classes allow matching only a specific set of characters.
A character class is created by placing characters inside square brackets [].

import re

pattern = r"[aeiou]"

if re.search(pattern, "grey"):
   print("Match 1")

if re.search(pattern, "qwertyuiop"):
   print("Match 2")

if re.search(pattern, "rhythm myths"):
   print("Match 3")

The pattern [aeiou] matches any string containing a vowel.

Character classes can also match ranges of characters:

• [a-z] matches any lowercase letter.
• [A-Z] matches any uppercase letter.
• [0-9] matches any digit.
• [A-Za-z] matches any letter (uppercase or lowercase).

import re

pattern = r"[A-Z][A-Z][0-9]"

if re.search(pattern, "LS8"):
   print("Match 1")

if re.search(pattern, "E3"):
   print("Match 2")

if re.search(pattern, "1ab"):
   print("Match 3")

To negate a character class (match anything except the specified characters), use ^ at the beginning.

import re

pattern = r"[^A-Z]"

if re.search(pattern, "this is all quiet"):
   print("Match 1")

if re.search(pattern, "AbCdEfG123"):
   print("Match 2")

if re.search(pattern, "THISISALLSHOUTING"):
   print("Match 3")

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Quantifiers

Quantifiers define how many times a pattern should be repeated.

Metacharacter	Meaning
*	Zero or more repetitions
+	One or more repetitions
?	Zero or one repetition
{x,y}	Between x and y repetitions

Example of * (zero or more repetitions):

import re

pattern = r"egg(spam)*"

if re.match(pattern, "egg"):
   print("Match 1")

if re.match(pattern, "eggspamspamegg"):
   print("Match 2")

if re.match(pattern, "spam"):
   print("Match 3")

Example of + (one or more repetitions):

import re

pattern = r"g+"

if re.match(pattern, "g"):
   print("Match 1")

if re.match(pattern, "gggggggggggggg"):
   print("Match 2")

if re.match(pattern, "abc"):
   print("Match 3")

Example of ? (zero or one repetition):

import re

pattern = r"ice(-)?cream"

if re.match(pattern, "ice-cream"):
   print("Match 1")

if re.match(pattern, "icecream"):
   print("Match 2")

if re.match(pattern, "sausages"):
   print("Match 3")

if re.match(pattern, "ice--ice"):
   print("Match 4")

Example of {x,y} (between x and y repetitions):

import re

pattern = r"9{1,3}$"

if re.match(pattern, "9"):
   print("Match 1")

if re.match(pattern, "999"):
   print("Match 2")

if re.match(pattern, "9999"):
   print("Match 3")

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Django

Prerequisites

Before starting, make sure you meet the following requirements:

• You are using PyCharm 2016.1 or later.
• You have at least Python 3.4.1 or later installed.
• You have Django 1.10.0 or later installed.
  If not, follow the guide:
  Installing Django in PyCharm

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Creating a New Django Project

All new projects are created in the same way:
Click Create New Project in the PyCharm Quick Start menu.

Then select Django, specify the Project Name and Location.

Best Practice: Use a Virtual Environment

Expand Project Interpreter: New Virtualenv Environment, select Virtualenv,
specify the location, and choose the base Python interpreter.

Expand More Settings and enter an Application Name.

Click Create – your Django project is ready.

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There is much more about Django project structure, database setup, running a server, creating models, and building views,
but due to the length of the document, let me know if you need further sections translated! 🚀