NHSDigital
diff --git a/‎codonPython/check_null.py‎
Lines changed: 10 additions & 4 deletions b/‎codonPython/check_null.py‎
Lines changed: 10 additions & 4 deletions
@@ -1,7 +1,7 @@
 import numpy
 import pandas as pd
 
-def check_null(dataframe: pd.DataFrame, columns_to_be_checked: list) -> bool:
+def check_null(dataframe: pd.DataFrame, columns_to_be_checked: tuple) -> bool:
     """
     Checks a pandas dataframe for null values
 
@@ -11,7 +11,7 @@ def check_null(dataframe: pd.DataFrame, columns_to_be_checked: list) -> bool:
     ----------
     data : pandas.DataFrame
         Dataframe to read
-    columns_to_be_checked: list
+    columns_to_be_checked: tuple
         Given dataframe columns to be checked for null values
 
     Returns
@@ -21,12 +21,18 @@ def check_null(dataframe: pd.DataFrame, columns_to_be_checked: list) -> bool:
 
     Examples
     --------
-    >>> check_null(dataframe = pd.DataFrame({'col1': [1,2], 'col2': [3,4]}), columns_to_be_checked = ['col1'])
+    >>> check_null(dataframe = pd.DataFrame({'col1': [1,2], 'col2': [3,4]}), columns_to_be_checked = ('col1'))
     0
-    >>> check_null(dataframe = pd.DataFrame({'col1': [1,numpy.nan], 'col2': [3,4]}), columns_to_be_checked = ['col1'])
+    >>> check_null(dataframe = pd.DataFrame({'col1': [1,numpy.nan], 'col2': [3,4]}), columns_to_be_checked = ('col1'))
     1
     """
 
+    for eachVal in columns_to_be_checked:
+        if type(eachVal) != str:
+            raise ValueError("Please input string values for column names.")
+    if columns_to_be_checked not in dataframe.columns:
+        raise KeyError("Please check the column names correspond to values in the DataFrame.")
+
     null_count = 0
     for eachColumn in columns_to_be_checked:
         prev_null_count = null_count