How to convert a string "-2" into float in python?

>>> a=("-2","-2")
>>> float(a[0][0])开发者_开发问答

This gives me an error

ValueError: invalid literal for float(): -

So how do I convert it ?

Use a[0] instead (a[0][0] is the first character of the first element, not the first element).

Sorry, but your code has an error:

float(a[0]) 

will do. If you need 2.2 as result, then

x = 0.0; # python 2.x
for i in range(0, len(a)):
    x += a[i] * 10**-i

It is one dimensional array, not multi dimensional array. So you have specify it as follows:

float(a[0])
float(a[1])

It can be specified that a[0] is the first place number '-2' and a[1] is the second place number '-2'. Try it.. I hope it should be helpful for you.

You're indexing incorrectly, if you want a tuple that contains floats for these two strings, then you have to do the following:

(float(a[0]), float(a[1]))

Note that the outer brackets are defining a new tuple.