You could use %g to achieve this:

'%g'%(3.140)

or, with Python ≥ 2.6:

'{0:g}'.format(3.140)

or, with Python ≥ 3.6:

f'{3.140:g}'

From the docs for format: g causes (among other things)

insignificant trailing zeros [to be] removed from the significand, and the decimal point is also removed if there are no remaining digits following it.

For Python versions in 2.6+ and 3.x

You can use the str.format method. Examples:

>>> print('{0:.16f}'.format(1.6))
1.6000000000000001

>>> print('{0:.15f}'.format(1.6))
1.600000000000000

Note the 1 at the end of the first example is rounding error; it happens because exact representation of the decimal number 1.6 requires an infinite number binary digits. Since floating-point numbers have a finite number of bits, the number is rounded to a nearby, but not equal, value.

For Python versions prior to 2.6 (at least back to 2.0)

You can use the "modulo-formatting" syntax (this works for Python 2.6 and 2.7 too):

>>> print '%.16f' % 1.6
1.6000000000000001

>>> print '%.15f' % 1.6
1.600000000000000

See PEP 3101:

'g' - General format. This prints the number as a fixed-point
      number, unless the number is too large, in which case
      it switches to 'e' exponent notation.

Old style (not preferred):

>>> "%g" % float(10)
'10'

New style:

>>> '{0:g}'.format(float(21))
'21'

New style 3.6+:

>>> f'{float(21):g}'
'21'

What you're asking for should be addressed by rounding methods like the built-in round function. Then let the float number be naturally displayed with its string representation.

>>> round(65.53, 4)  # num decimal <= precision, do nothing
'65.53'
>>> round(40.355435, 4)  # num decimal > precision, round
'40.3554'
>>> round(0, 4)  # note: converts int to float
'0.0'

Python only displays what's needed, so it displated 10.0

If it's the matter of printing it as 10.00.

To do that.

>>> d = 10
>>> print "Value: %.2f" % float(d)
Value: 10.00
>>>