Python float to string precision

I have a floating point number, say 135.12345678910. I want to concatenate that value to a string, but only want 135.123456789. With print, I can easily do this by doing something like:

print "%.9f" % numvar

with numvar being my original number. Is there an easy way to do this?

asked Mar 7, 2013 at 5:14

1

With Python < 3 (e.g. 2.6 [see comments] or 2.7), there are two ways to do so.

# Option one
older_method_string = "%.9f" % numvar

# Option two
newer_method_string = "{:.9f}".format(numvar)

But note that for Python versions above 3 (e.g. 3.2 or 3.3), option two is preferred.

For more information on option two, I suggest this link on string formatting from the Python documentation.

And for more information on option one, this link will suffice and has info on the various flags.

Python 3.6 (officially released in December of 2016), added the f string literal, see more information here, which extends the str.format method (use of curly braces such that f"{numvar:.9f}" solves the original problem), that is,

# Option 3 (versions 3.6 and higher)
newest_method_string = f"{numvar:.9f}"

solves the problem. Check out @Or-Duan's answer for more info, but this method is fast.

answered Mar 7, 2013 at 5:36

jyalimjyalim

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4

Using round:

>>> numvar = 135.12345678910
>>> str(round(numvar, 9))
'135.123456789'

answered Mar 7, 2013 at 5:33

shantanooshantanoo

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0

In case the precision is not known until runtime, this other formatting option is useful:

>>> n = 9
>>> '%.*f' % (n, numvar)
'135.123456789'

answered Aug 17, 2015 at 7:04

Yu HaoYu Hao

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It's not print that does the formatting, It's a property of strings, so you can just use

newstring = "%.9f" % numvar

answered Mar 7, 2013 at 5:19

John La RooyJohn La Rooy

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To set precision with 9 digits, get:

print "%.9f" % numvar

Return precision with 2 digits:

print "%.2f" % numvar 

Return precision with 2 digits and float converted value:

numvar = 4.2345
print float("%.2f" % numvar) 

Eric Aya

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answered Jan 18, 2018 at 8:13

Tejas TankTejas Tank

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The str function has a bug. Please try the following. You will see '0,196553' but the right output is '0,196554'. Because the str function's default value is ROUND_HALF_UP.

>>> value=0.196553500000 
>>> str("%f" % value).replace(".", ",")

answered Nov 9, 2015 at 16:33

ethemsulanethemsulan

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