A Byte of Python

• Written by Swaroop Chitlur
• All my slides for teaching Python are adapted from this book!
• Licensed under a Creative Commons License
• Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License
• https://python.swaroopch.com/

Comments

• Use # for comments
• They can be above:

  # Note that print is a function 
  print('hello world') 
  

• Or at the end

  print('hello world')  # Note that print is a function
  

Literal Constants

• Numbers: 5, 1.23
• Strings: 'This is a string', "It's a string!"
• Boolean: True, False
• Nothing!: None

Numbers

Numbers are mainly of two types - integers and floats.

Integers

• An example of an integer is 2 which is just a whole number.

Floats

• Examples of floating point numbers ("floats") are 3.23 and 52.3e-4.
• The e notation indicates powers of 10. 52.3e-4 => 52.3 * 10^-4^.

Strings

• Strings are used to represent text.
• You can use single quotes, double quotes, or triple quotes for multi-line strings.

  'Hello'
  "Hello"
  '''
  This is a
  multi-line string
  '''
  

Strings (continued)

• Strings are immutable (more on that later)
• Use the format method:

  name = 'Swaroop'
  age = 20
  print(f'{name} was {age} years old')
  

Escape Sequences

• Use \ for escape sequences
• Examples:
  • \' for single quote
  • \" for double quote
  • \\ for backslash
  • \n for newline
  • \t for tab

Escape Sequences

>>> print("foo")
foo

>>> print("foo\nbar")
foo
bar

>>> print("foo\n\nbar")
foo

bar

Variables

• Variables store information

  >> i = 5
  >> print(i)
  5
  >> i = i + 1
  >> print(i)
  6
  

Variables Rules

• The first character of the identifier must be a letter of the alphabet or an underscore (_).
• The rest of the identifier name can consist of letters (uppercase ASCII or lowercase ASCII or Unicode character), underscores (_) or digits (0-9).
• Identifier names are case-sensitive. For example, myname and myName are not the same.

Variable Name Examples

• age, name, foo, bar
• age2, name_2, foo_bar
• _age, _name - starting with _ denotes "private"
• AGE, NAME - ALL_CAPS denotes "constant"
• i, j, k - common for iterators in loops (more on this later)
• df, x, y, X, Y - bad variables but common in data science

Variables Contain Both Data and Types

>>> i = 5
>>> type(i)
<class 'int'>
>>> i = 'foo'
>>> type(i)
<class 'str'>

Logical and Physical Lines

• Logical line: single statement
• Physical line: what you see in the editor

i = 5
print(i)

i = 5; print(i)

Indentation

• Whitespace at the beginning of the line
• Determines grouping of statements
• Use four spaces for indentation

  if True:
      print('True')
  else:
      print('False')
  

Exercise: Variables

1. Assign your name and age to variables.
2. Calculate how many years it will be until you are 100 years old in a new variable.
3. Print your name, your age, and the number of years until you are 100.