I am struggling to understand why this function apparently fails in the Jupyter Notebook, but not in the IPython shell:
def present_value( r, n, fv = None, pmt = None ):
'''
Function to compute the Present Value based on interest rate and
a given future value.
Arguments accepted
------------------
* r = interest rate,
which should be given in its original percentage, eg.
5% instead of 0.05
* n = number of periods for which the cash flow,
either as annuity or single flow from one present value
* fv = future value in dollars,
if problem is annuity based, leave this empty
* pmt = each annuity payment in dollars,
if problem is single cash flow based, leave this empty
'''
original_args = [r, n, fv, pmt]
dec_args = [Decimal( arg ) if arg != None
else arg
for arg in original_args
]
if dec_args[3] == None:
return dec_args[2] / ( ( 1 + ( dec_args[0] / 100 ) )**dec_args[1] )
elif dec_args[2] == None:
# annuity_length = range( 1, dec_args[1] + 1 )
# Not allowed to add a Decimal object
# with an integer and to use it
# in the range() function,
# so we dereference the integer from original_args
annuity_length = range( 1, original_args[1] + 1 )
# Apply discounting to each annuity payment made
# according to number of years left till end
all_compounded_pmt = [dec_args[3] * ( 1 / ( ( 1 + dec_args[0] / 100 ) ** time_left ) ) \
for time_left in annuity_length
]
return sum( all_compounded_pmt )
When I imported the module that this function resides in, named functions.py, using from functions import *, and then executed present_value(r=7, n=35, pmt = 11000), I got the error:
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-93-c1cc587f7e27> in <module>()
----> 1 present_value(r=7, n=35, pmt = 11000)
/path_to_file/functions.py in present_value(r, n, fv, pmt)
73 if dec_args[3] == None:
74 return dec_args[2]/((1 + (dec_args[0]/100))**dec_args[1])
---> 75
76 elif dec_args[2] == None:
77 # annuity_length = range(1, dec_args[1]+1)
TypeError: 'decimal.Decimal' object cannot be interpreted as an integer
but in the IPython shell, evaluating this function it works perfectly fine:
In [42]: functions.present_value(r=7, n=35, pmt = 11000)
Out[42]: Decimal('142424.39530474029537')
Can anyone please help me with this really confusing and obscure issue?
