Python basics flash cards

The cards, front and back

1. 1
   Front

   print()

   Back

   Displays output on the screen.

   print('Hello, world') shows Hello, world.

2. 2
   Front

   Variable

   Back

   A name that stores a value. Python creates it when you assign to it with =.

   score = 10

3. 3
   Front

   Basic data types

   Back

   • int: whole numbers, such as 42
   • float: decimals, such as 3.14
   • str: text in quotes, such as 'cat'
   • bool: True or False
4. 4
   Front

   input()

   Back

   Reads a line typed by the user and always returns it as a string.

   name = input('Your name? ')

5. 5
   Front

   Type conversion

   Back

   Change a value's type with int(), float() or str().

   age = int(input('Age? ')) turns the typed text into a whole number.

6. 6
   Front

   Arithmetic operators

   Back

   • + add, - subtract, * multiply, / divide (gives a float)
   • // floor division (whole-number result)
   • % modulus (remainder)
   • ** power: 2 ** 3 is 8
7. 7
   Front

   Comparison operators

   Back

   == equal, != not equal, < less than, > greater than, <= and >=. Each comparison gives True or False.

8. 8
   Front

   if, elif, else

   Back

   Run code only when a condition is True.

   if score >= 50:

       print('Pass')

   else:

       print('Try again')

9. 9
   Front

   Indentation

   Back

   Python uses indentation (usually four spaces) to show which lines belong to a block, such as the body of an if, loop or function. Wrong indentation causes an IndentationError.

10. 10
    Front

    for loop

    Back

    Repeats code for each item in a sequence.

    for i in range(3):

        print(i)

    prints 0, 1 and 2.

11. 11
    Front

    range()

    Back

    Produces a sequence of numbers. range(5) gives 0 to 4; range(2, 6) gives 2 to 5; range(0, 10, 2) gives even numbers 0 to 8.

12. 12
    Front

    while loop

    Back

    Repeats code as long as a condition stays True. Make sure the condition eventually becomes False, or the loop never ends.

13. 13
    Front

    List

    Back

    An ordered, changeable collection in square brackets.

    fruits = ['apple', 'pear']

    fruits.append('plum') adds an item.

14. 14
    Front

    Indexing

    Back

    Items are numbered from 0. fruits[0] is the first item and fruits[-1] is the last.

15. 15
    Front

    len()

    Back

    Returns the number of items in a list or characters in a string.

    len('cards') is 5.

16. 16
    Front

    Dictionary

    Back

    Stores key and value pairs in curly braces.

    ages = {'Ana': 15, 'Ben': 16}

    ages['Ana'] gives 15.

17. 17
    Front

    Tuple

    Back

    An ordered collection in round brackets that cannot be changed after it is created.

    point = (3, 4)

18. 18
    Front

    Defining a function

    Back

    Use def, a name, brackets for parameters and a colon.

    def greet(name):

        return 'Hi ' + name

19. 19
    Front

    return

    Back

    Sends a value back from a function to the code that called it. A function with no return gives None.

20. 20
    Front

    f-string

    Back

    A string with an f before the quote that inserts values inside curly braces.

    f'You scored {score} points'

21. 21
    Front

    try and except

    Back

    Handles errors without crashing.

    try:

        n = int(text)

    except ValueError:

        print('Not a number')

22. 22
    Front

    Comment

    Back

    A note for humans that Python ignores. It starts with #.

    # work out the total