python中如何将字符串强制转为数字

class int(x, base=10)

>>> s1 = '999'

>>> if s1.isdigit():

      num1 = int(s1)

>>> type(num1)

<class 'int'>

>>> num1

999

class float([x])

>>> s2 = '999.888'

>>> if s2.isdigit():

      num2 = float(s2)

>>> type(num2)

Traceback (most recent call last):

  File "<pyshell#53>", line 1, in <module>

    type(num2)

NameError: name 'num2' is not defined

>>>

>>> s2.isdigit()

False

>>> s2 = '999.888'

>>> num2 = float(s2)

>>> type(num2)

<class 'float'>

>>> num2

999.888

>>>