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Formatting floating point


On 9/4/19 1:25 PM, Chris Angelico wrote:
> On Thu, Sep 5, 2019 at 3:16 AM Dave via Python-list
> <python-list at python.org> wrote:
>>
>> All,
>>
>> I have been going in circles trying to format a floating point number so
>> there is only 1 decimal place.  In reading all of the gobble-gook that
>> passes for Python advice, it looked like I should have done this:
>>
>> numStr = '3.14159'
>> num = float(numstr)     # OK so far
>> numFmt = format(num, '{0:.1f}')         # Errors on format string
>> # --- Alternative that also does not work
>> numFmt = float("{0:.1f}".format(numStr))
>> # ---
>> numFmt = format(num, '0.1f')            # Does work
>>
> 
> Let's start by eliminating a few possibilities here. Don't try
> formatting the original string, and don't call float() on the result
> afterwards; just start with a floating-point value, and then create a
> formatted string. If you think about starting with a value (which in
> this case is a number) and the need to make a displayable version
> (which implies that it's a string), your options basically look like
> this:
> 
> num = 3.14159
> num_fmt = format(num, ".1f")
> num_fmt = "{0:.1f}".format(num)
> num_fmt = f"{num:.1f}"
> 
> All of these will give you back the string "3.1". All of them involve
> a format string of ".1f", and they differ only in how they're choosing
> which value to put there.
> 
> Hopefully that will clear things up a bit.
> 
> ChrisA
> 

That helps!  Thanks Chris.

Dave,