Do the second one, just don’t worry about rounding it. Let the formatting do the rounding for display.

Include the type specifier in your format expression:

>>> a = 10.1234
>>> f'{a:.2f}'
'10.12'

What you’re seeing is still rounding, it’s just not the rounding you’re expecting. Python by default rounds ties to even, instead of always rounding up, because rounding up on ties creates specific biases in the data (so does rounding ties to even, but these biases are less problematic, as they don’t affect the overall distribution).

As an example:

nums = [1.5, 2.5, 3.5, 4.5]
[round(x) for x in nums]
# [2, 2, 4, 4]

The same is true for more decimal points:

nums = [0.25, 0.75]
[round(x, 1) for x in nums]
# [0.2, 0.8]

Including 0.05, 0.15 … in the list above would yield surprising results, since these decimal floating-point values can’t be exactly represented as binary floating-point values, so they’re not exactly even; for example, 0.05 is stored as approximately 0.05000000000000000278…, so it won’t be rounded down to (even) 0.0, but rather up, to (odd) 0.1.

You are running into the old problem with floating point numbers that not all numbers can be represented exactly. The command line is just showing you the full floating point form from memory.

With floating point representation, your rounded version is the same number. Since computers are binary, they store floating point numbers as an integer and then divide it by a power of two so 13.95 will be represented in a similar fashion to 125650429603636838/(2**53).

Double precision numbers have 53 bits (16 digits) of precision and regular floats have 24 bits (8 digits) of precision. The floating point type in Python uses double precision to store the values.

For example,

>>> 125650429603636838/(2**53)
13.949999999999999

>>> 234042163/(2**24)
13.949999988079071

>>> a = 13.946
>>> print(a)
13.946
>>> print("%.2f" % a)
13.95
>>> round(a,2)
13.949999999999999
>>> print("%.2f" % round(a, 2))
13.95
>>> print("{:.2f}".format(a))
13.95
>>> print("{:.2f}".format(round(a, 2)))
13.95
>>> print("{:.15f}".format(round(a, 2)))
13.949999999999999

If you are after only two decimal places (to display a currency value, for example), then you have a couple of better choices:

1. Use integers and store values in cents, not dollars and then divide by 100 to convert to dollars.
2. Or use a fixed point number like decimal.

You can use the round function, which takes as its first argument the number and the second argument is the precision after the decimal point.

In your case, it would be:

answer = str(round(answer, 2))