complex([real[, imag]])
中文說明：
建立一個值為real + imag * j的複數或者轉化一個字串或數為複數。如果第一個引數為字串，則不需要指定第二個引數。
引數real: int, long, float或字串；
引數imag: int, long, float。
英文說明：
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.
程式碼例項：
>>> complex(1, 2)
(1 + 2j)
#數字
>>> complex(1)
(1 + 0j)
#當做字串處理
>>> complex("1")
(1 + 0j)
#注意：這個地方在“+”號兩邊不能有空格，也就是不能寫成"1 + 2j"，應該是"1+2j"，否則會報錯
>>> complex("1+2j")
(1 + 2j)