Formatted strings for rounding in python

Question

I want to round a integer using formatted strings, but it has to be via a parameter asked. I have the following code where p is the amount of decimals to be rounded to.

def fahrenheit_to_celsius(t, p):
    celsius = ((t - 32.0) * 5.0 / 9.0)

    print "%f "%(celsius)

Answer 1

def fahrenheit_to_celsius(t, p):
    celsius = (t - 32.) * 5. / 9.
    return "{0:.{1}f}".format(celsius, p)

print fahrenheit_to_celsius(76.2, 2) # prints "24.56"
print fahrenheit_to_celsius(0, 0) # prints "-18"

Answer 2

In the format specifier, add .* between % and f. '.' specifying decimals, '*' specifying width to be picked from argument list.

def fahrenheit_to_celsius(t, p):
    celsius = ((t - 32.0) * 5.0 / 9.0)

    print "%.*f"%(p,celsius) ## pick width from argument.
    print "%.2f"%(celsius) ## always 2 decimals

From the printf manual page:

The field width

An optional decimal digit string (with non-zero first digit) specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given). Instead of a decimal digit string one may write "*" or "*m$" (for some decimal integer m) to specify that the field width is given in the next argument, or in the m-th argument, respectively, which must be of type int. A negative field width is taken as a '-' flag followed by a positive field width. In no case does a nonexistent or small field width cause truncation of a field; if the result of a conversion is wider than the field width, the field is expanded to contain the conversion result.

Answer 3

>>> def f_to_c(t, p=0):
...     return round(((t - 32.0) * 5.0 / 9.0), p)
... 
>>> print("{}".format(f_to_c(10, 2)))
-12.22