How do I convert a string to a double in Python?

Question

I would like to know how to convert a string containing digits to a double.

Solution 1

>>> x = "2342.34"
>>> float(x)
2342.3400000000001

There you go. Use float (which behaves like and has the same precision as a C,C++, or Java double).

Solution 2

The decimal operator might be more in line with what you are looking for:

>>> from decimal import Decimal
>>> x = "234243.434"
>>> print Decimal(x)
234243.434

Solution 3

Be aware that if your string number contains more than 15 significant digits float(s) will round it.In those cases it is better to use Decimal

Here is an explanation and some code samples: https://docs.python.org/3/library/sys.html#sys.float_info

Comments

[Admin]

That is not a python double. A python double has unlimited capacity.

[habnabit]

Or, more specifically, Python floats are C doubles.

[Evorlor]

Bah used float instead of double. now my code is off by .0000000001 which hurts

[drevicko]

incidentally, this also works with exponent notation. eg: float('7.5606e-08') produces the expected python float.

[Bruce_Warrior]

With my python (version 2.7.10), when I assign >>> x = "2342.34" and convert to float >>> float(x) I get 2342.34 instead the 2342.3400000000001 reported by @Mongoose

[user1510539]

Use >>> 0.1 + 0.2 for double. >>> 0.1 + 0.6 for float.

[mendel]

The returned thing is a Decimal(...), not a simple number.