Got things to work finally.

Still things to do (one bug discovered, see TODOs)

SimpleStockData.py

@@ -3,7 +3,7 @@ import pandas as pd
 
 
 class SimpleStockData:
-    def __init__(self, ticker_list: list, period_start: str, period_end: str, to_currency: str = ""):
+    def __init__(self, ticker_list: list, period_start: str, period_end: str, to_currency: str, ohcl: str = "Close"):
         """
         :param period_start:
             start date (format YYYY-MM-DD)
@@ -11,14 +11,16 @@ class SimpleStockData:
             end date (format YYYY-MM-DD)
         :param ticker_list:
             list containing all stocks/exchange rates (yfinance considers both as "Tickers")
+            Example: []
         :param to_currency:
-            currency to convert rates to
+            currency to convert rates to (e.g. EUR)
         """
 
         self.ticker_list = ticker_list
-        self.to_currency = to_currency
+        self.to_currency = to_currency.upper()  # make it uppercase
         self._period_start = period_start
         self._period_end = period_end
+        self._ohcl = ohcl.capitalize()
 
         self._exchange_df = None  # Mapping: time mapped to conversion factor, to get the right converted value per date
         self._create_exchange_dataframe()  # initialize self.exchange_df attribute
@@ -43,7 +45,7 @@ class SimpleStockData:
         The mapping is recreated by this function following the information in the
         _from_currency_list.
         return:
-            boolean
+            boolean - success or not
         """
 
         # check if a to_currency is even given
@@ -54,26 +56,29 @@ class SimpleStockData:
         _from_currency_list = []
         for i in range(len(self.ticker_list)):  # to get all indexes; this adds an entry for each currency
             add_currency = f"{self.get_info(i, 'currency')}{self.to_currency}=X"  # Format: "fffttt=X" f=from, t=to
+            add_currency = add_currency.upper()  # make everything uppercase
             # for the case that FROM and TO are equal, just don't download the data (as conversion factor's 1)
             if add_currency == f"{self.to_currency}{self.to_currency}=X":
                 pass
             elif add_currency not in _from_currency_list:  # add a new item if not already there
                 _from_currency_list.append(add_currency)
 
-            print(_from_currency_list)
-
         # now the real process begins
         tickers = yf.Tickers(" ".join(_from_currency_list))  # create a new Ticker instance with all wanted currencies
-        exchange_rates = []
-        for i in tickers.tickers:  # get all the history of each currency conversion factors
-            # for simplicity: using the conversion factor of closing (.Close at the end)
-            exchange_rates.append(tickers.tickers[i].history(start=self._period_start, end=self._period_end).Close)
 
-        self._exchange_df = pd.DataFrame(
+        exchange_rates = []  # temporary variable where all exchange rates are stored in (as objects of pd.Series)
-            exchange_rates).T  # transpose the dataframe (imagine just switching rows and columns)
+        for er_name in tickers.tickers:  # get all the history of each currency conversion factors
-        self._exchange_df.columns = _from_currency_list  # set the right names for the columns in the dataframe
+            # for simplicity: using the conversion factor of closing (.Close at the end)
-        self._exchange_df[
+            exchange_rates.append((tickers.tickers[er_name].history(start=self._period_start, end=self._period_end)[self._ohcl], er_name))
-            f"{self.to_currency}{self.to_currency}=X"] = 1.0  # for FROM and TO being equal: set factor to 1
+            # now exchange_rates contains tuples of the form (ticker, er_name) where er_name is the name of the
+            # currency ticker, used only internal in this method (_from_currency_list variable). The index is now taken
+            # to set the right names for every row in the dataframe
+
+        # now, the rates are taken from the exchange_rates list and are all wrapped up in a beautiful DataFrame
+        self._exchange_df = pd.DataFrame()
+        for exchange_rate, er_name in exchange_rates:
+            self._exchange_df[er_name] = exchange_rate
+        self._exchange_df[f"{self.to_currency}{self.to_currency}=X"] = 1.0  # for FROM and TO being equal: set factor to 1
 
         return True
 
@@ -102,20 +107,45 @@ class SimpleStockData:
         :param convert:
             decides if the resulting values should be converted to the specified to_convert currency (given at
             object creation)
-        :return: pandas.DataFrame
+        :return: pandas.DataFrame (with extra columns for the converted value if wanted)
         """
 
-        # TODO: Not working. Something is wrong with the access to the _exchange_df via [].
+        result = self._get_history(idx, interval)[self._ohcl].to_frame()
-
-        result = self._get_history(idx, interval)
         result["Ticker Index"] = idx
-        ticker_currency = self.get_info(idx, "currency")
+        ticker_currency = self.get_info(idx, "currency").upper()  # upper it as sometimes it doesn't fit
 
         if convert:
-            value_list = ["Open", "High", "Low", "Close"]
+            exrate_name = f"{ticker_currency}{self.to_currency}=X"
-            for value in value_list:
+            result["ex_rate_name"] = exrate_name
-                result["rating_name"] = f"{ticker_currency}{self.to_currency}=X"
+            ex_rate_series = self._exchange_df[exrate_name]
-                result["rating"] = self._exchange_df[f"{ticker_currency}{self.to_currency}=X"]
+
-                result[f"{value}.conv"] = result[value] / result["rating"]
+            # now there's a result dataframe with ticker, currency, rate name etc. as column names
+            # to add only matching ex rates per day (sometimes there are more days with exchange rates recorded than
+            # share prices), the result df has to be transposed so that the following function df.append can select
+            # by columns. TODO: implement the bug fix when not the exact same timestamps and amount of data are given in both the series and the df
+            """
+            result = result.T
+
+            ex_rate_df = ex_rate_df.to_list()
+            print(ex_rate_df)
+            result.append(ex_rate_df[result.columns], ignore_index=True)  # magic - see above :)
+            result = result.T  # transpose back
+            result[f"{self._ohcl} in {self.to_currency}"] = result[self._ohcl] / result["ex_rate"]
+            """
+
+            result["ex_rate"] = ex_rate_series.to_list()
+            result[f"{self._ohcl} in {self.to_currency}"] = result[self._ohcl] / result["ex_rate"]
+
 
         return result
+
+
+def test():
+    ssd = SimpleStockData(["RHM.DE", "BAS.DE", "AZN.L"], "2024-01-02", "2024-01-18", "EUR")
+    print(ssd.get_info(0))
+    print(ssd.get_info(1))
+    print(ssd.get_info(2))
+
+    print(ssd.get_history(0))
+    print(ssd.get_history(1))
+    print(ssd.get_history(2))