calling variable inside string returns ValueError

Question

I'm trying to define these two variables, and then use them again in line 6. However, I get the following error when running. This only seems to happen with pandas.date_range. My end goal is to run this as a .py file to produce a chart.

start_date = raw_input('enter start date: ')
end_date = raw_input('enter end date: ')

dataPR['date'] = pd.DatetimeIndex(dataPR['intake_date']).date
grouped_dataPR = dataPR.groupby(['date']).sum()
idx = pd.date_range(start='%s', end='%s') % (start_date, end_date)
grouped_dataPR.index = pd.DatetimeIndex(grouped_dataPR.index)
grouped_dataPR = grouped_dataPR.reindex(idx, fill_value=0)
grouped_dataPR['date'] = grouped_dataPR.index
dataPR_df = pd.DataFrame([grouped_dataPR])
ts = pd.Series(grouped_dataPR['count'], index=grouped_dataPR.index)
ts.plot()
pd.rolling_mean(ts,30).plot(style='k')

Error:

ValueError                                Traceback (most recent call            last)
<ipython-input-33-2ac5fe9d8951> in <module>()
  2 grouped_dataPR = dataPR.groupby(['date']).sum()
  3 #idx = pd.date_range('%s', '%s' % (start_date, end_date))
----> 4 idx = pd.date_range(start='%s', end='%s') % (start_date,     end_date)
      5 grouped_dataPR.index = pd.DatetimeIndex(grouped_dataPR.index)
      6 grouped_dataPR = grouped_dataPR.reindex(idx, fill_value=0)

/Users/abc/anaconda/lib/python2.7/site-    packages/pandas/tseries/index.pyc in date_range(start, end, periods,     freq, tz, normalize, name, closed, **kwargs)
   1921     return DatetimeIndex(start=start, end=end,     periods=periods,
   1922                          freq=freq, tz=tz,     normalize=normalize, name=name,
-> 1923                          closed=closed, **kwargs)
   1924 
   1925 

/Users/abc/anaconda/lib/python2.7/site-    packages/pandas/util/decorators.pyc in wrapper(*args, **kwargs)
     87                 else:
     88                     kwargs[new_arg_name] = new_arg_value
---> 89             return func(*args, **kwargs)
     90         return wrapper
     91     return _deprecate_kwarg

/Users/abc/anaconda/lib/python2.7/site-    packages/pandas/tseries/index.pyc in __new__(cls, data, freq, start, end,     periods, copy, name, tz, verify_integrity, normalize, closed, ambiguous,     dtype, **kwargs)
    235             return cls._generate(start, end, periods, name,     freq,
    236                                  tz=tz, normalize=normalize,     closed=closed,
--> 237                                  ambiguous=ambiguous)
    238 
    239         if not isinstance(data, (np.ndarray, Index,     ABCSeries)):

/Users/abc/anaconda/lib/python2.7/site-    packages/pandas/tseries/index.pyc in _generate(cls, start, end, periods,     name, offset, tz, normalize, ambiguous, closed)
    377 
    378         if start is not None:
--> 379             start = Timestamp(start)
    380 
    381         if end is not None:

pandas/tslib.pyx in pandas.tslib.Timestamp.__new__     (pandas/tslib.c:8973)()

pandas/tslib.pyx in pandas.tslib.convert_to_tsobject     (pandas/tslib.c:22522)()

pandas/tslib.pyx in pandas.tslib.convert_str_to_tsobject     (pandas/tslib.c:24520)()

ValueError:

What inputs are you using? E.g. what is start_date and end_date? What format does Timestamp need? — Tom Dalton
– Tom Dalton, Commented Jan 27, 2016 at 18:14
% is a string operator; you can't use it with an arbitrary block of syntax. — chepner
– chepner, Commented Jan 27, 2016 at 18:22

Josh · Accepted Answer · 2016-01-27 18:16:05Z

4

You should call the variables directly, without wrapping them in quotes. You're attempting to do string substitution in a funny way that won't work.

idx = pd.date_range(start=start_date, end=end_date)

If for some reason you still want to do string substitution, you would have to do it like this, substituting each string individually:

idx = pd.date_range(start='%s' % (start_date, ), end='%s' % (end_date, ))

answered Jan 27, 2016 at 18:16

Josh

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Comments

OneCricketeer · Accepted Answer · 2016-01-27 18:29:39Z

3

I think you just need to do

pd.date_range(start=start_date, end=end_date)

Reason being is that pandas.data_range expects a string or datetime-like object for both the start and end parameters. '%s' is not datetime-like.

If that was a valid option, however, the code you wrote is trying to do a modulo operation between the pandas date_range and a tuple of strings, which more than likely throws some other error.

If you did need to use string formatting for those values, I would suggest using the new way of string formatting like

pd.date_range(start='{}'.format(start_date), end='{}'.format(end_date))

edited Jan 27, 2016 at 18:29

answered Jan 27, 2016 at 18:15

OneCricketeer

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2 Comments

chepner Over a year ago

The ValueError occurs when something in Pandas finally tries to use the literal strings %s that date_range receives as arguments. Python doesn't even get as far as trying to evaluate the % operator.

ik629 Over a year ago

this works! - thank you so much for your help. I can't believe I hadn't tried that.

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