The basics of syntax
INPUT · Slides
01 / 06
Sometimes you need two conditions together — "18 or over and under 65". For that, join them with and.
and is True only when both hold. If either one fails, it is False.
age = 30if age >= 18 and age < 65: print("standard")Result
standard
02 / 06
When either will do — "Saturday or Sunday" — use or.
or is True if at least one of them holds. Both holding is fine too.
day = "sat"if day == "sat" or day == "sun": print("day off")Result
day off
03 / 06
Most other languages use the symbols && and ||. Python uses the words and and or.
Read if age >= 18 and age < 65: out loud and it is very nearly an English sentence. Python caring about readability shows up here as well.
print(True and False)print(True or False)Result
False True
04 / 06
not turns a condition inside out. True becomes False and False becomes True.
Useful, but overusing it makes things hard to read. x != 5 is tidier than not x == 5, is it not? If the opposite condition is easy to write, write that instead.
print(not True)stock = 0if not stock > 0: print("sold out")Result
False sold out
05 / 06
For "when x is 1 or 2" you will be tempted to write if x == 1 or 2:. That does not do what you think.
Python reads it as (x == 1) or (2), which holds no matter what x is. Each side of an or needs a complete condition of its own.
x = 5if x == 1 or x == 2: print("1 or 2")else: print("neither")Result
neither
06 / 06
"At least 10 and at most 20" can actually be written 10 <= x <= 20, exactly the way you would in maths.
Very few languages allow that. 10 <= x and x <= 20 works too, but the first one is the Python way.
x = 15if 10 <= x <= 20: print("in range")Result
in range