Python Basics

Python stores values in variables, works them out with operators in a fixed order, and has four basic types: int, float, str and bool.

Key ideas

• Python works out ** first, then *, /, // and %, then + and −, going left to right; brackets come before all of them.
• // gives the whole-number part of a division and % the remainder; / always gives a float.
• Every value has a type: int (7), float (3.5), str ('7') or bool (True, False).
• input() always gives text (a str); use int() or float() to turn it into a number.
• + adds numbers but joins strings; a string times a whole number repeats it.
• x += 3 is short for x = x + 3; likewise x *= 2 and x //= 4.

Remember

Watch out

• Doing + before *: 5 + 3 * 2 is 11, not 16.
• Forgetting that / prints a decimal: 10 / 5 is 2.0, not 2.
• Doing arithmetic on input() without int(): typing 5 for a = input() makes a * 2 print 55.

Worked example