6是python格式浮点的默认十进制数字吗？

Question

I'm learning the format method in python and tried to convert 1 to a float by it.

"{:f}".format(1)

But why is the output '1.000000' instead of '1.0' ?

Answer 1

I suppose this is the default output if you do not specify the number of decimals. Using the 3.6+ f-string format:

f'{1.123456789:f}'
'1.123457'

f'{1:.1f}'
'1.0'

f'{1.12345678901234567:.10f}'
'1.1234567890'

Now a whole other question is what is the precision of a floating point number, for example

f'1.1:.20f'
'1.10000000000000008882'

which seems to suggest a floating point gives up to 16 decimal accuracy. If you need more then you need to use the Decimal module Decimal fixed point and floating point arithmetic

Answer 2

The Python documentation says for formatting with f “Displays the number as a fixed-point number. The default precision is 6.”

Note that not all Python implementations use the same format for floating-point. As the documentation notes , most modern machines use IEEE-754 floating-point arithmetic, and almost all platforms map Python float objects to IEEE-754 basic 64-bit binary format, but this is not guaranteed.