pythonlistformattingprecisionfloating-point-conversion

Convert a list of float to string in Python

I have a list of floats in Python and when I convert it into a string, I get the following

[1883.95, 1878.3299999999999, 1869.4300000000001, 1863.4000000000001]

These floats have 2 digits after the decimal point when I created them (I believe so),

Then I used

str(mylist)

How do I get a string with 2 digits after the decimal point?

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Let me be more specific, I want the end result to be a string and I want to keep the separators:

"[1883.95, 1878.33, 1869.43, 1863.40]"

I need to do some string operations afterwards. For example +="!\t!".

Inspired by @senshin the following code works for example, but I think there is a better way

msg = "["

for x in mylist:
    msg += '{:.2f}'.format(x)+','

msg = msg[0:len(msg)-1]
msg+="]"
print msg
Solution

  • Use string formatting to get the desired number of decimal places.

    >>> nums = [1883.95, 1878.3299999999999, 1869.4300000000001, 1863.4000000000001]
>>> ['{:.2f}'.format(x) for x in nums]
['1883.95', '1878.33', '1869.43', '1863.40']

    The format string {:.2f} means "print a fixed-point number (f) with two places after the decimal point (.2)". str.format will automatically round the number correctly (assuming you entered the numbers with two decimal places in the first place, in which case the floating-point error won't be enough to mess with the rounding).