PySchools Python Quick Reference Guide

Variables and Data Types

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Variables and Data Types

To declare variables in Python:

>>> a = 3       # assign the integer value 3 to the variable a
>>> b = 4.0     # assign the decimal value 4.0 to the variable b
>>> c = '1'     # assign the string '1' to the variable c
>>> a + b       # adding two numbers
7.0
>>> a + c       # adding number and string (This is not allowed and will produce an error)

Commonly used data types include int, float, str and bool. To determine the datatype of a variable:

>>> a = 3
>>> type(a)
<type 'int'>
>>> b = 4.0
<type 'float'>
>>> c = 'hello'
>>> type(c)
<type 'str'>
>>> d = True
>>> type(d)
<type 'bool'>

Conversion between Data Types

Use the following functions for conversion between data types: float(x),int(x), str(x)

>>> a = 5           # int
>>> b = float(a)    # convert to float
>>> b
5.0
>>> c = str(a)      # convert to string
>>> c
'5'
>>> d = int(4.6)    # convert to int, take note of the round down
>>> d
4

Mathematical operations

For numbers, the usual mathematical rules apply. You can use any of the following operations: *, /, +, - on numbers. Take note of the division operator.

>>> 1/2     # returns integer value
0
>>> 1/2.0   # returns decimal value
0.5

Take note of the following operations on string

>>> '1' + '2'   # concatenation instead of addition
'12'
>>> '1' * 5     # This is valid in Python
'11111'

Summary of Mathematical Operators

Symbols Operations Examples Outputs
+ Addition a = 1+2 3
- Subtraction a = 2-1 1
* Multiplication a = 2*2 4
/ Division a = 5.0/2 2.5
// Truncating Division a = 5.0//2 2.0
% Modulo a = 5%2 1
** Power a = 5**2 25

See also

Ready for some practice? Test your understanding at PySchools: Variables and Datatypes.

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