So I understand how to *use* something like the below to change the way pandas prints numbers:

pd.set_option('display.float_format', '{:,}'.format)

or

pd.set_option('display.float_format', '{:,.2f}'.format)

But I don't understand what that second argument actually is. The documentation says

" The callable should accept a floating point number and return a string with the desired format of the number. This is used in some places like SeriesFormatter. "

So I assume the second argument needs to be something that returns a string, but then I don't understand how this other example I see a lot works. My understanding of lambda functions is that they're anonymous functions, but how does the below return a string?

pd.set_option('display.float_format', lambda x: '%.5f' % x)

Can someone walk me through how pandas parses that second argument into a number format?

)

Relatedly, I also discovered that

def bfunc(num):
return('%.5f' % num)

actually returns a number with the format I want (essentially the lambda function above)...But why? What did the % sign do here? I thought that was for like template literals in Python/inserting variables into strings. What does .5f mean under the hood here if I do %.5f?