complex([real[, imag]])
中文说明：
创建一个值为real + imag * j的复数或者转化一个字符串或数为复数。如果第一个参数为字符串，则不需要指定第二个参数。
参数real: int, long, float或字符串；
参数imag: int, long, float。
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英文说明：
Create a complex number with the value real + imag*j 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 function serves as a numeric conversion function like int(), long() 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, long, complex.
代码实例：
>>> complex(1, 2)
(1 + 2j)
#数字
>>> complex(1)
(1 + 0j)
#当做字符串处理
>>> complex("1")
(1 + 0j)
#注意：这个地方在“+”号两边不能有空格，也就是不能写成"1 + 2j"，应该是"1+2j"，否则会报错
>>> complex("1+2j")
(1 + 2j) 
