One of the most important features of any programming language is its ability to manipulate variables. A variable
is just a name that refers to a value; you can think of a variable as a box that stores a piece of data.
In Python, the basic data types are strings and numbers. There are two types of numbers:
integers (both positive and negative) and floats (fractional numbers with a decimal point).
You can assign numbers to variables very easily. Try running the following program:
a = 324
b = 24
c = a - b
print 'a - b is', c
In the above code, a, b, and c are all integers, and 'a - b is' is a string. The result
of this program is to print:
You can now use all common arithmetic operations involving numbers:
- Addition:
2 + 3 == 5
- Subtraction:
5 - 2 == 3
- Multiplication:
3 * 4 == 12
- Division:
15 / 3 == 5
- Division remainder:
18 % 5 == 3
- Exponentiation:
2 ** 3 == 8
It is important to note that if you try to divide two integers, Python always rounds
down the result (so 18/5 == 3
).
To obtain a precise result for this division, you need to indicate floating point division;
either of the following expressions results in a "float" data type:
18.0/5 == 3.6
or float(18)/5 == 3.6
In Python, the single equals sign (=
) means "assign a value to a variable". For
example, a = 3
assigns 3 to the integer a. In order to denote equality, Python uses
the double equals sign (==
).
In Python, a string is an ordered sequence of letters, numbers and other characters.
You can create string variables just like you did with :
Notice that the string must be surrounded by " or ' (but not a mix of both).
You can use quotes inside the string, as long as you use the opposite type of
quotes to surround the string, e.g., a = "Monty Python's Flying Circus"
or b = 'Project "Rosalind"'
.
String operations differ slightly from operations on numbers:
a = 'Rosalind'
b = 'Franklin'
c = '!'
print a + ' ' + b + c*3
Output: