Number and String data types

• Numbers
• String
• Constants
• Built-in Operators

Variable data type is automatically determined by Python. They only need to be assigned some value before using it elsewhere - like print function or part of expression

Numbers

• Integer examples

>>> num1 = 7
>>> num2 = 42
>>> total = num1 + num2
>>> print(total)
49
>>> total
49

# no limit to integer precision, only limited by available memory
>>> 34 ** 32
10170102859315411774579628461341138023025901305856

# using single / gives floating point output
>>> 9 / 5
1.8

# using double / gives only the integer portion, no rounding
>>> 9 // 5
1

>>> 9 % 5
4

• Floating point examples

>>> appx_pi = 22 / 7
>>> appx_pi
3.142857142857143

>>> area = 42.16
>>> appx_pi + area
45.30285714285714

>>> num1
7
>>> num1 + area
49.16

• the E scientific notation can be used as well

>>> sci_num1 = 3.982e5
>>> sci_num2 = 9.32e-1
>>> sci_num1 + sci_num2
398200.932

>>> 2.13e21 + 5.23e22
5.443e+22

• Binary numbers are prefixed with 0b or 0B (i.e digit 0 followed by lower/upper case letter b)
• Octal numbers are prefixed with 0o or 0O (i.e digit 0 followed by lower/upper case letter o)
• Similarly, Hexadecimal numbers are prefixed with 0x or 0X

>>> bin_num = 0b101
>>> oct_num = 0o12
>>> hex_num = 0xF

>>> bin_num
5
>>> oct_num
10
>>> hex_num
15

>>> oct_num + hex_num
25

• _ can be used between digits for readability
  • introduced in Python v3.6

>>> 1_000_000
1000000
>>> 1_00.3_352
100.3352
>>> 0xff_ab1
1047217

# f-strings formatting explained in a later chapter
>>> num = 34 ** 32
>>> print(f'{num:_}')
10_170_102_859_315_411_774_579_628_461_341_138_023_025_901_305_856

Further Reading

• Python docs - numbers
• decimal
• fractions
• complex
• Python docs - keywords - do not use these as variables

String

• strings can be declared using single or double quotes
• Use \ to escape quotes which are part of string itself if the string contains both single and double quotes

>>> str1 = 'This is a string'
>>> str1
'This is a string'
>>> greeting = "Hello World!"
>>> greeting
'Hello World!'

>>> weather = "It's a nice and warm day"
>>> weather
"It's a nice and warm day"
>>> print(weather)
It's a nice and warm day

>>> weather = 'It\'s a nice and warm day'
>>> print(weather)
It's a nice and warm day

• Escape sequences like newline character \n can be used within string declaration

>>> colors = 'Blue\nRed\nGreen'
>>> colors
'Blue\nRed\nGreen'

>>> print(colors)
Blue
Red
Green

• Use r prefix (stands for raw) if you do not want escape sequences to be interpreted
• It is commonly used with regular expressions, see Pattern matching and extraction for examples

>>> raw_str = r'Blue\nRed\nGreen'
>>> print(raw_str)
Blue\nRed\nGreen

# to see how the string is stored internally
>>> raw_str
'Blue\\nRed\\nGreen'

• String concatenation and repetition

>>> str1 = 'Hello'
>>> str2 = ' World'
>>> print(str1 + str2)
Hello World

>>> style_char = '-'
>>> style_char * 10
'----------'

>>> word = 'buffalo '
>>> print(word * 8)
buffalo buffalo buffalo buffalo buffalo buffalo buffalo buffalo 

# Python v3.6 allows variable interpolation with f-strings
>>> msg = f'{str1} there'
>>> msg
'Hello there'

• Triple quoted strings
• like single line strings, """ or ''' can be used as required as well as escape characters using \

#!/usr/bin/python3

"""
This line is part of multiline comment

This program shows examples of triple quoted strings
"""

# assigning multiple line string to variable
poem = """\
The woods are lovely, dark and deep,   
But I have promises to keep,   
And miles to go before I sleep,   
And miles to go before I sleep.
"""

print(poem, end='')

• Triple quoted strings also help in documentation, see Docstrings chapter for examples

$ ./triple_quoted_string.py 
The woods are lovely, dark and deep,   
But I have promises to keep,   
And miles to go before I sleep,   
And miles to go before I sleep.
$

Further Reading

• Python docs - strings
• Python docs - f-strings - for more examples and caveats
• Python docs - List of Escape Sequences and more info on strings
• Python docs - Binary Sequence Types
• formatting triple quoted strings

Constants

Paraphrased from Python docs - constants

• None The sole value of the type NoneType
  • None is frequently used to represent the absence of a value
• False The false value of the bool type
• True The true value of the bool type
• Python docs - Truth Value Testing

>>> bool(2)
True
>>> bool(0)
False
>>> bool('')
False
>>> bool('a')
True

Built-in Operators

• arithmetic operators
  • + addition
  • - subtraction
  • * multiplication
  • / division (float output)
  • // division (integer output, result is not rounded)
  • ** exponentiation
  • % modulo
• string operators
  • + string concatenation
  • * string repetition
• comparison operators
  • == equal to
  • > greater than
  • < less than
  • != not equal to
  • >= greater than or equal to
  • <= less than or equal to
• boolean logic
  • and logical and
  • or logical or
  • not logical not
• bitwise operators
  • & and
  • | or
  • ^ exclusive or
  • ~ invert bits
  • >> right shift
  • << left shift
• and many more...

Further Reading

• Python docs - Numeric types - complete list of operations and precedence
• Python docs - String methods