在 Python 中的小数点后向浮点数添加零

Question

I am reading in data from a file, modify it and write it to another file. The new file will be read by another program and therefore it is crucial to carry over the exact formatting

for example, one of the numbers on my input file is:

1.000000

my script applies some math to the columns and should return

2.000000

But what is currently returned is

2.0

How would I write a float for example my_float = 2.0 , as my_float = 2.00000 to a file?

Answer 1

Format it to 6 decimal places:

format(value, '.6f')

Demo:

>>> format(2.0, '.6f')
'2.000000'

The format() function turns values to strings following the formatting instructions given.

Answer 2

From Python 3.6 it's also possible to do f-string formatting. This looks like:

f"{value:.6f}"

Example:

> print(f"{2.0:.6f}")
'2.000000'

Answer 3

I've tried n ways but nothing worked that way I was wanting in, at last, this worked for me.

foo = 56
print (format(foo, '.1f'))
print (format(foo, '.2f'))
print (format(foo, '.3f'))
print (format(foo, '.5f'))

output:

56.0 
56.00
56.000
56.00000

Meaning that the 2nd argument of format takes the decimal places you'd have to go up to. Keep in mind that format returns string.

Answer 4

An answer using the format() command is above, but you may want to look into the Decimal standard library object if you're working with floats that need to represent an exact value. You can set the precision and rounding in its context class, but by default it will retain the number of zeros you place into it:

>>> import decimal
>>> x = decimal.Decimal('2.0000')
>>> x
Decimal('2.0000')
>>> print x
2.0000
>>> print "{0} is a great number.".format(x)
2.0000 is a great number.

Answer 5

I've had problems with using variables in f strings. When all else fails, read the manual :)

"A consequence of sharing the same syntax as regular string literals is that characters in the replacement fields must not conflict with the quoting used in the outer formatted string literal."

https://docs.python.org/3/reference/lexical_analysis.html#f-strings

Case in point:

my_number = 90000
zeros = '.2f'

my_string = f"{my_number:,{zeros}}"

print (my_string)
90,000.00

my_string = f'{my_number:,{zeros}}'

will not work, because of the single quotes.

Quotes containing the f string and the string variable used in the f string should be different .

If using single quotes for the string variable, use double quotes for the f module and vice versa.