add missing type hints

app/data/dataframe_util.py

@@ -18,7 +18,7 @@ def stats(data: DataFrame, num: str, den: str, frac: str) -> List[float]:
 def get_time_range(data: DataFrame, ts_col: str) -> Tuple[str, str]:
     return f"{data[ts_col].min():%d/%m/%Y}" , f"{data[ts_col].max():%d/%m/%Y}"
 
-def get_divider(width: int, marker="─"):
+def get_divider(width: int, marker:str = "─") -> str:
     if width <= 3:
         return " ─ "
 
@@ -26,7 +26,7 @@ def get_divider(width: int, marker="─"):
     ex = marker if (width % 2) and plen > 0 else ""
     return f" {{p:>{plen}}}{ex}{{p:<{plen}}} ".format(p=marker)
 
-def get_caption(time_range: Tuple[str, str], width: int):
+def get_caption(time_range: Tuple[str, str], width: int) -> str:
     left, right = time_range
     pad = width - len(left) - len(right)
     return ''.join([