How to convert float to fixed point decimal in python

Question

I have some library function foo, that returns a floating point value with two decimal places (representing a price). I have to pass to to other function bar which expects a Decimal with fixed point for two decimal places.

value = foo() # say value is 50.15
decimal_value = decimal.Decimal(value) # Not expected. decimal_value contains Decimal('50.14999999999999857891452847979962825775146484375')
bar(decimal_value) # Will not work as expected

# One possible solution
value = foo() # say value is 50.15
decimal_value = decimal.Decimal(str(round(value,2))) # Now decimal_value contains Decimal('50.15') as expected
bar(decimal_value) # Will work as expected

Question:

How to convert arbitrary float to fixed Decimal point with 2 decimal places? And without intermediate string conversion using str.

I am not worried about the performance. Just want to confirm if intermediate str conversion is the pythonic way.

Update: Other Possible Solutions

# From selected answer
v = 50.15
d = Decimal(v).quantize(Decimal('1.00'))

# Using round (Does not work in python2)
d = round(Decimal(v), 2)

Solution

Use Decimal.quantize:

Return a value equal to the first operand after rounding and having the exponent of the second operand.

>>> from decimal import Decimal
>>> Decimal(50.15)
Decimal('50.14999999999999857891452847979962825775146484375')
>>> Decimal(50.15).quantize(Decimal('1.00'))
Decimal('50.15')

Unlike the bad str approach, this works for any number:

>>> decimal.Decimal(str(50.0))
Decimal('50.0')
>>> decimal.Decimal(50.0).quantize(decimal.Decimal('1.00'))
Decimal('50.00')

Comments

[Mark Dickinson]

I like the round solution, as its easier to read and write than the quantize-base solution. But bear in mind it only works on Python 3: on Python 2, rounding a Decimal instance gives a float back.

[balki]

Thanks! Edited to make a note.

[Christian Dean]

But why not just str? Is there a compelling reason to user Decimal.quantize over str?

[Antti Haapala -- Слава Україні]

@ChristianDean because str is not guaranteed to give 2 decimal places.

[Christian Dean]

Ah, I see. I didn't know that.