Python - question about decimal arithmetic

Question

I have 3 questions pertaining to decimal arithmetic in Python, all 3 of which are best asked inline:

1)

>>> from decimal import getcontext, Decimal
>>> getcontext().prec = 6
>>> Decimal('50.567898491579878') * 1
Decimal('50.5679')
>>> # How is this a precision of 6? If the decimal counts whole numbers as
>>> # part of the precision, is that actually still precision?
>>> 

and

2)

>>> from decimal import getcontext, Decimal
>>> getcontext().prec = 6
>>> Decimal('50.567898491579878')
Decimal('50.567898491579878')
>>> # Shouldn't that have been rounded to 6 digits on instantiation?
>>> Decimal('50.567898491579878') * 1
Decimal('50.5679')
>>> # Instead, it only follows my precision setting set when operated on.
>>> 

3)

>>> # Now I want to save the value to my database as a "total" with 2 places.
>>> from decimal import Decimal
>>> # Is the following the correct way to get the value into 2 decimal places,
>>> # or is there a "better" way?
>>> x = Decimal('50.5679').quantize(Decimal('0.00'))
>>> x  # Just wanted to see what the value was
Decimal('50.57')
>>> foo_save_value_to_db(x)
>>> 

Answer 1

1. Precision follows sig figs, not fractional digits. The former is more useful in scientific applications.

2. Raw data should never be mangled. Instead it does the mangling when operated upon.

3. This is how it's done.