Python内置函数(13)-complex

官方文档

class complex([real[, imag]])

Return a complex number with the value real + imag*1j or convert a string or number to a complex number. If the first parameter is a string, it will be interpreted as a complex number and the function must be called without a second parameter. The second parameter can never be a string. Each argument may be any numeric type (including complex). If imag is omitted, it defaults to zero and the constructor serves as a numeric conversion like int and float. If both arguments are omitted, returns 0j.

Note

When converting from a string, the string must not contain whitespace around the central + or - operator. For example, complex('1+2j') is fine, but complex('1 + 2j') raises ValueError.

The complex type is described in Numeric Types — int, float, complex.

Changed in version 3.6: Grouping digits with underscores as in code literals is allowed.

说明：1.函数功能，返回一个复数，有2个可选参数

         2.当两个参数都不提供时，返回复数0j

>>> complex()
0j

         3.当第一参数为字符串时，调用时不能传第二个参数。此时字符串参数，需是一个能表示复数的字符串，而且加减号左右不能有空格

#第一个参数为字符串时，调用不能传第二个参数
>>> complex('1+2j',2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: complex() can't take second arg if first is a string

#加减号左右不能有空格
>>> complex('1 + 2j')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: complex() arg is a malformed string


>>> complex('1+2j')
(1+2j)

        4.当第一个参数为int或者float时，第二个参数可为空，表示虚部为0。如果提供第二个参数，则第二个参数也需要为int或者float

ret = complex(123)
print(ret)
#输出  (123+0j)

ret = complex(2.14,-3.16)
print(ret)
#输出  (2.14-3.16j)