First question in SO, still learning python & pandas
EDIT: I've successfully pivoted the values DF to go from long to wide in order to have unique id+date indices (e.g. no uniqueID has more than 1 row per day). However, I've stil not been able to achieve my desired result.
I have a couple of DFs that I want to merge based on A) uniqueID and B) if that uniqueID is contemplated in between different and multiple ranges of dates. I found this question which approaches to what I'm looking for; however, after the solution isn't viable and digging a bit it would appear as if what I'm attempting isn't possible due to dates overlap (?)
The gist of this would be to: add up all the values on the df_values if the uniqueID is in the df_dates_range and its corresponding day column is within the start:end range from dates_ranges.
There are many more columns in each of the DFs, but these are the relevant ones. Imply duplicates everwhere and no particular orders. All the DF series are formated appropriately.
So, here's df1, dates_range:
import pandas as pd
import numpy as np
dates_range = {"uniqueID": [1, 2, 3, 4, 1, 7, 10, 11, 3, 4, 7, 10],
               "start": ["12/31/2019", "12/31/2019", "12/31/2019", "12/31/2019", "02/01/2020", "02/01/2020", "02/01/2020", "02/01/2020", "03/03/2020", "03/03/2020", "03/03/2020", "03/03/2020"],
               "end": ["01/04/2020", "01/04/2020", "01/04/2020", "01/04/2020", "02/05/2020", "02/05/2020", "02/05/2020", "02/05/2020", "03/08/2020", "03/08/2020", "03/08/2020", "03/08/2020"],
               "df1_tag1": ["v1", "v1", "v1", "v1", "v2", "v2", "v2", "v2", "v3", "v3", "v3", "v3"]}
df_dates_range = pd.DataFrame(dates_range, 
                              columns = ["uniqueID", 
                                         "start", 
                                         "end", 
                                         "df1_tag1"])
df_dates_range[["start","end"]] = df_dates_range[["start","end"]].apply(pd.to_datetime, infer_datetime_format = True)
And df2, values:
values = {"uniqueID": [1, 2, 7, 3, 4, 4, 10, 1, 8, 7, 10, 9, 10, 8, 3, 10, 11, 3, 7, 4, 10, 14], 
          "df2_tag1": ["abc", "abc", "abc", "abc", "abc", "def", "abc", "abc", "abc", "abc", "abc", "abc", "def", "def", "abc", "abc", "abc", "def", "abc", "abc", "def", "abc"], 
          "df2_tag2": ["type 1", "type 1", "type 2", "type 2", "type 1", "type 2", "type 1", "type 2", "type 2", "type 1", "type 2", "type 1", "type 1", "type 2", "type 1", "type 1", "type 2", "type 1", "type 2", "type 1", "type 1", "type 1"], 
          "day": ["01/01/2020", "01/02/2020", "01/03/2020", "01/03/2020", "01/04/2020", "01/04/2020", "01/04/2020", "02/01/2020", "02/02/2020", "02/03/2020", "02/03/2020", "02/04/2020", "02/05/2020", "02/05/2020", "03/03/2020", "03/04/2020", "03/04/2020", "03/06/2020", "03/06/2020", "03/07/2020", "03/06/2020", "04/08/2020"],
          "df2_value1": [2, 10, 6, 5, 7, 9, 3, 10, 9, 7, 4, 9, 1, 8, 7, 5, 4, 4, 2, 8, 8, 4], 
          "df2_value2": [1, 5, 10, 13, 15, 10, 12, 50, 3, 10, 2, 1, 4, 6, 80, 45, 3, 30, 20, 7.5, 15, 3], 
          "df2_value3": [0.547, 2.160, 0.004, 9.202, 7.518, 1.076, 1.139, 25.375, 0.537, 7.996, 1.475, 0.319, 1.118, 2.927, 7.820, 19.755, 2.529, 2.680, 17.762, 0.814, 1.201, 2.712]}
values["day"] = pd.to_datetime(values["day"], format = "%m/%d/%Y")
df_values = pd.DataFrame(values, 
                         columns = ["uniqueID", 
                                    "df2_tag1", 
                                    "df2_tag2", 
                                    "day", 
                                    "df2_value1", 
                                    "df2_value2", 
                                    "df2_value1"])
Going from the first link, I tried running the following:
df_dates_range.index = pd.IntervalIndex.from_arrays(df_dates_range["start"], 
                                                        df_dates_range["end"], 
                                                        closed = "both")
df_values_date_index = df_values.set_index(pd.DatetimeIndex(df_values["day"]))
df_values = df_values_date_index["day"].apply( lambda x : df_values_date_index.iloc[df_values_date_index.index.get_indexer_non_unique(x)])
However, I get this error. n00b checked, got rid of the second to last day indices and the issue persisted:
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-58-54ea384e06f7> in <module>
     14 df_values_date_index = df_values.set_index(pd.DatetimeIndex(df_values["day"]))
     15 
---> 16 df_values = df_values_date_index["day"].apply( lambda x : df_values_date_index.iloc[df_values_date_index.index.get_indexer_non_unique(x)])
C:\anaconda\lib\site-packages\pandas\core\series.py in apply(self, func, convert_dtype, args, **kwds)
   3846             else:
   3847                 values = self.astype(object).values
-> 3848                 mapped = lib.map_infer(values, f, convert=convert_dtype)
   3849 
   3850         if len(mapped) and isinstance(mapped[0], Series):
pandas\_libs\lib.pyx in pandas._libs.lib.map_infer()
<ipython-input-58-54ea384e06f7> in <lambda>(x)
     14 df_values_date_index = df_values.set_index(pd.DatetimeIndex(df_values["day"]))
     15 
---> 16 df_values = df_values_date_index["day"].apply( lambda x : df_values_date_index.iloc[df_values_date_index.index.get_indexer_non_unique(x)])
C:\anaconda\lib\site-packages\pandas\core\indexes\base.py in get_indexer_non_unique(self, target)
   4471     @Appender(_index_shared_docs["get_indexer_non_unique"] % _index_doc_kwargs)
   4472     def get_indexer_non_unique(self, target):
-> 4473         target = ensure_index(target)
   4474         pself, ptarget = self._maybe_promote(target)
   4475         if pself is not self or ptarget is not target:
C:\anaconda\lib\site-packages\pandas\core\indexes\base.py in ensure_index(index_like, copy)
   5355             index_like = copy(index_like)
   5356 
-> 5357     return Index(index_like)
   5358 
   5359 
C:\anaconda\lib\site-packages\pandas\core\indexes\base.py in __new__(cls, data, dtype, copy, name, tupleize_cols, **kwargs)
    420             return Index(np.asarray(data), dtype=dtype, copy=copy, name=name, **kwargs)
    421         elif data is None or is_scalar(data):
--> 422             raise cls._scalar_data_error(data)
    423         else:
    424             if tupleize_cols and is_list_like(data):
TypeError: Index(...) must be called with a collection of some kind, Timestamp('2020-01-01 00:00:00') was passed
The expected result whould be:
desired = {"uniqueID": [1, 2, 3, 4, 1, 7, 10, 11, 3, 4, 7, 10],
           "start": ["12/31/2019", "12/31/2019", "12/31/2019", "12/31/2019", "02/01/2020", "02/01/2020", "02/01/2020", "02/01/2020", "03/03/2020", "03/03/2020", "03/03/2020", "03/03/2020"],
           "end": ["01/04/2020", "01/04/2020", "01/04/2020", "01/04/2020", "02/05/2020", "02/05/2020", "02/05/2020", "02/05/2020", "03/08/2020", "03/08/2020", "03/08/2020", "03/08/2020"],
           "df1_tag1": ["v1", "v1", "v1", "v1", "v2", "v2", "v2", "v2", "v3", "v3", "v3", "v3"],
           "df2_tag1": ["abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc"],
           "df2_value1": [2, 10, 5, 16, 10, 7, 5, np.nan, 11, 8, 2, 8], 
           "df2_value2+df2_value3": [1.547, 7.160, 22.202, 33.595, 75.375, 17.996, 8.594,  np.nan, 120.501, 8.314, 37.762, 16.201], 
           "df2_tag3": ["abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc", "abc"]}
df_desired = pd.DataFrame(desired, 
                          columns = ["uniqueID", 
                                     "start", 
                                     "end", 
                                     "df1_tag1", 
                                     "df2_tag1", 
                                     "df2_value1", 
                                     "df2_value2+df2_value3", 
                                     "df2_tag3"])
df_desired[["start","end"]] = df_desired[["start","end"]].apply(pd.to_datetime, infer_datetime_format = True)
or in graphic visualization:
Notice how column S & T @ row 10 are NaN because uniqueID 11 had no "activity" during the v2 period; however, I'd love to be able to pull the tags from df2 if possible somehow; they're 100% there, just maybe not for that period, maybe a task for a second script? Also, notice that col T is aggregation of cols J+K
EDIT: forgot to mention I had previously attempted to do this using @firelynx 's solution on this question, but despite my 32gb ram, my machine couldn't cope. The SQL solution didn't work for me because of some, had sqlite3 library issues

 
    