if else not checking both of the conditions in Python

Question

i want new column ['pred_n'] to be created based on certain condition, condition is as follows: if year is less than or equal to current year & month is less than current month, pred_n should be equal to yhatpct else it should be yhatpct_ft. trying following syntax:

if((dfyz['year_x'] < datetime.now().year) | ((dfyz['year_x'] == datetime.now().year) & (dfyz['mon'] < datetime.now().month))):
    dfyz['pred_n'] = dfyz['yhat']*dfyz['pct']
else:
    dfyz['pred_n'] = dfyz['yhat']*dfyz['pct_ft']

but output shows only if condition though in my data I have month and year from 2019 - 08 onwards and if i use

if ((dfyz['year_x'] < datetime.now().year) | ((dfyz['year_x'] == datetime.now().year) & (dfyz['mon'] < datetime.now().month))):
     dfyz['pred_n'] = dfyz['yhat']*dfyz['pct']
elif (((dfyz['year_x'] == datetime.now().year) & (dfyz['mon'] >= datetime.now().month)) | ((dfyz['year_x'] > datetime.now().year))):
       dfyz['pred_n'] = dfyz['yhat']*dfyz['pct_ft']

it gives output only for else condition

Use or instead of | and and instead of & in Python expressions. Also consider writing now = datetime.now() and replacing all those calls in the expressions. Together, these will make your logic much easier to read (and reason about)”. — Kirk Strauser
– Kirk Strauser, Commented Sep 16, 2021 at 1:38
with or, and it shows following error ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all(). — Ashish
– Ashish, Commented Sep 16, 2021 at 1:46
Decompose your conditions using variables (also helps to fix now() to a definite point in time for all your comparisons). Choose the variable names wisely so the expresisons are easier to read. And yes, Python logical opertors are and or not — Marcello Romani
– Marcello Romani, Commented Sep 16, 2021 at 1:51

donkopotamus · Accepted Answer · 2021-09-16 01:39:49Z

2

You are currently using the bitwise operators | and &, rather than the logical operators orand and. Presumably you really want something like:

now = datetime.now()
if (dfyz['year_x'] < now.year or        
    dfyz['year_x'] == now.year and dfyz['mon'] < now.month
):
    ...

(Its not great practice to keep calling now several times ... each of your calls is potentially returning a different value for now)

answered Sep 16, 2021 at 1:39

donkopotamus

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1 Comment

Ashish Over a year ago

or, and it shows following error ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all(). now = datetime.now() if ((dfyz['year_x'] < now.year) or ((dfyz['year_x'] == now.year) and (dfyz['mon'] < now.month))): dfyz['pred_n'] = dfyz['yhat']*dfyz['pct'] elif (((dfyz['year_x'] == now.year) and (dfyz['mon'] >= now.month)) or ((dfyz['year_x'] > now.year))): dfyz['pred_n'] = dfyz['yhat']*dfyz['pct_ft']

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