How can I understand using of complex() function?

In python documentation it is wrote for built-in function complex([real[imag]]):

..or convert a string or number to a complex number.

But when I try:

>>开发者_运维问答;> complex('string')

I get:

  Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
  ValueError: complex() arg is a malformed string

I don't understand something. I will be glad if someone tells me what is about? Sorry if this question is simple, but i just start to learn python.

complex is a data type for complex numbers.

http://en.wikipedia.org/wiki/Complex_number

Examples on constructing them:

>>> complex(1, 2)
(1+2j)
>>> complex('1+2j')
(1+2j)
>>> complex(0)
0j
>>> complex(1)
(1+0j)
>>> complex(1) + complex(0, 1)
(1+1j)

If you aren't familiar with complex or imaginary numbers, you can probably just move on and not worry about any of this. =)

The complex function is used for working with complex numbers (http://en.wikipedia.org/wiki/Complex_number), of the form a+bj. So you can use it like this:

>>> a = complex("1+2j")
>>> a
(1+2j)
>>> a*a
(-3+4j)

"string" isn't a complex number. The proper usage is as follows:

>>> a = complex('3j')
>>> a
3j
>>> b = 4 + a
>>> b
(4+3j)

'string' is not a number. It's not anything like a number.

How can you compute a complex value of string? It's not a number

Try using numbers or string representations of numbers

complex(2)
complex('3')