lesson 10 Variables & Data Types · beginner

None and type

type() tells you what kind of value a name holds. None means there is no value.

You'll be able to

Read the kind of a value with type()
Store None when a value is missing
Tell text, numbers, True, and None apart by their kinds

The idea

"12", 12, and 12.0 can look alike in a print. type() reports the kind. You will see the word class and then str for text, int for a whole number, float for a decimal, or bool for True and False. When a program misbehaves, asking for the kind is often the fastest way to see why.

Run each example to see what it prints. Running examples doesn't count toward progress.

example-1.py · Four kinds

print(type("12"))
print(type(12))
print(type(12.0))
print(type(True))

None means no value. A missing coupon, a missing note, a city that was not set. It is not the text "None", and it is not 0 or False. type(None) reports NoneType.

example-2.py · Nothing stored yet

coupon = None
print(coupon)
print(type(coupon))

Mistake to avoid: coupon = "None" prints exactly the same word as coupon = None. Only type() shows the difference: the first is str, a piece of text that happens to spell None.

Review

type() prints the kind: str, int, float, bool, or NoneType.
None means there is no value. It is not the text "None".
"12" and 12 look alike when printed. Their kinds are str and int. Next module: operators that compute with these values.

Practise this