Python

Using python to interact with OS

Virtual Environment

$ pip install virtualenv

$ python3 -m venv env
$ source env/bin/activate
(env) $ deactivate

Division (/) always returns a float. To do floor division and get an integer result (discarding any fractional result) you can use the // operator; to calculate the remainder you can use %:

In interactive mode, the last printed expression is assigned to the variable _. This means that when you are using Python as a desk calculator, it is somewhat easier to continue calculations,

>>> price * tax
12.5625
>>> price + _
113.0625
>>> round(_, 2)
113.06

strings, which can be expressed in several ways. They can be enclosed in single quotes ('...') or double quotes ("...") with the same result 2. \ can be used to escape quotes

Two or more string literals (i.e. the ones enclosed between quotes) next to each other are automatically concatenated

concatenate variables or a variable and a literal, use +

Note that since -0 is the same as 0, negative indices start from -1.

In addition to indexing, slicing is also supported. While indexing is used to obtain individual characters, slicing allows you to obtain substring:>>>

>>> word[0:2]  # characters from position 0 (included) to 2 (excluded)
'Py'
>>> word[2:5]  # characters from position 2 (included) to 5 (excluded)
'tho'

Regular Expression

Regular Expression HOWTO — Python 3.10.2 documentation

the regular expression test will match the string test exactly. (You can enable a case-insensitive mode that would let this RE match Test or TEST as well; more about this later.)

Here’s a complete list of the metacharacters; their meanings will be discussed in the rest of this HOWTO.

. ^ $ * + ? { } [ ] \ | ( )

A Regular Expression (RegEx) is a sequence of characters that defines a search pattern. For example,

^a...s$

The above code defines a RegEx pattern. The pattern is: any five letter string starting with a and ending with s.

import re

txt = "The rain in Spain"
x = re.search("^The.*Spain$", txt)


pattern = '^a...s$'
test_string = 'abyss'
result = re.match(pattern, test_string)

if result:
  print("Search successful.")
else:
  print("Search unsuccessful.")	

Python RegEx (With Examples)