int(x, [base])
功能：函数的作用是将一个数字或base类型的字符串转换成整数。
int(x=0)
int(x, base=10)，base缺省值为10，也就是说不指定base的值时，函数将x按十进制处理。
Python2.x
Python3.x
1. x 可以是数字或字符串，但是base被赋值后 x 只能是字符串
2. x 作为字符串时必须是 base 类型，也就是说 x 变成数字时必须能用 base 进制表示
class int(x=0)
class int(x, base=10)
Return an integer object constructed from a number or string x, or return 0 if no arguments are given. If x is a number, return x.__int__(). For floating point numbers, this truncates towards zero.
If x is not a number or if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in radix base. Optionally, the literal can be preceded by + or - (with no space in between) and surrounded by whitespace. A base-n literal consists of the digits 0 to n-1, with a to z (or A to Z) having values 10 to 35. The default base is 10. The allowed values are 0 and 2–36. base-2, -8, and -16 literals can be optionally prefixed with 0b/0B, 0o/0O, or 0x/0X, as with integer literals in code. base 0 means to interpret exactly as a code literal, so that the actual base is 2, 8, 10, or 16, and so that int('010', 0) is not legal, while int('010') is, as well as int('010', 8).
The integer type is described in Numeric Types — int, float, complex.
Changed in version 3.4: If base is not an instance of int and the base object has a base.__index__ method, that method is called to obtain an integer for the base. Previous versions used base.__int__ instead of base.__index__.
Changed in version 3.6: Grouping digits with underscores as in code literals is allowed.
int(3.14) # 3 int(2e2) # 200 int(100, 2) # 出错，base 被赋值后函数只接收字符串
int('23', 16) # 35
int('Pythontab', 8) # 出错，Pythontab不是个8进制数 int('FZ', 16) # 出错，FZ不能用十六进制表示
int('FZ', 36) # 575 int('0x10', 16) # 16，0x是十六进制的符号
int('0x10', 17) # 出错，'0x10'中的 x 被视作英文字母 x
int('0x10', 36) # 42804，36进制包含字母 x原文来源：https://m.pythontab.com/article/1134
