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.

That is not a python double. A python double has unlimited capacity. — , Feb 26 '10 at 20:55

score 391 · Answer 1 · edited Jan 04 '19 at 05:45

391

>>> 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).

edited Jan 04 '19 at 05:45

Byte11

answered Jan 27 '09 at 05:49

Mongoose

51

Or, more specifically, Python floats are C doubles. – habnabit Jan 27 '09 at 05:54
1

Bah used float instead of double. now my code is off by .0000000001 which hurts – Evorlor Jan 18 '14 at 19:24
2

incidentally, this also works with exponent notation. eg: `float('7.5606e-08')` produces the expected python float. – drevicko Feb 13 '14 at 07:33
2

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 – Bruce_Warrior Aug 31 '15 at 20:21
Use `>>> 0.1 + 0.2` for double. `>>> 0.1 + 0.6` for float. – user1510539 Sep 04 '17 at 10:03

score 57 · Answer 2 · answered Jun 17 '11 at 11:56

57

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

answered Jun 17 '11 at 11:56

foomip

1

The returned thing is a Decimal(...), not a simple number. – mendel Oct 05 '21 at 07:23

score 5 · Answer 3 · answered Jan 25 '18 at 01:11

5

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

answered Jan 25 '18 at 01:11

user1767754

3 Answers3