Create self-function and get ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()

Question

I create a function like below:

import pandas as pd
DATAPATH = "path/"

df_orig = pd.read_csv(DATAPATH + "file.csv" , dtype=str, sep = "|")

def test(df = None, df2 = None):
    if df == None:
        pass
    elif not isinstance(df, pd.DataFrame):
        df_in = pd.read_csv(DATAPATH + df + ".csv", dtype=str, sep = "|")
        print(f'============ Number of obs. in {df} ============\n{df_in.shape[0]:,}\n')
        print(f'============ First 10 Records of {df}.csv ============\n{df_in.head(10)}\n\n\n')
        print(f'============ Last 10 Records of {df}.csv ============\n{df_in.tail(10)}\n\n\n')
    else:
        df_in = df
        print(f'============ Number of obs. ============\n{df_in.shape[0]:,}\n')
        print(f'============ First 10 Records ============\n{df_in.head(10)}\n\n\n')
        print(f'============ Last 10 Records ============\n{df_in.tail(10)}\n\n\n')

    if df2 == None:
        pass
    elif not isinstance(df2 , pd.DataFrame):
        df_in2 = pd.read_csv(DATAPATH + df2 + ".csv", dtype=str, sep = "|")
        print(f'============ Number of obs. in {df2} ============\n{df_in2.shape[0]:,}\n')
        print(f'============ First 10 Records of {df2}.csv ============\n{df_in2.head(10)}\n\n\n')
        print(f'============ Last 10 Records of {df2}.csv ============\n{df_in2.tail(10)}\n\n\n')
    else:
        df_in2 = df2
        print(f'============ Number of obs. ============\n{df_in2.shape[0]:,}\n')
        print(f'============ First 10 Records ============\n{ddf_in2_in.head(10)}\n\n\n')
        print(f'============ Last 10 Records ============\n{df_in2.tail(10)}\n\n\n')


test(df = df_orig, df2 = None)

However, I got the error:

Traceback (most recent call last):
  File "test.py", line 21, in <module>
    test(df = df_orig)
  File "test.py", line 7, in test
    if df == None:
  File "/mypath/anaconda3/lib/python3.7/site-packages/pandas/core/generic.py", line 1443, in __nonzero__
    f"The truth value of a {type(self).__name__} is ambiguous. "
ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

Any suggestion on this?
Do I use the wrong logic for if df == None:?

Answer 1

The official way of checking if DataFrames are empty:

if df.empty:
    # do something

Another way is to check the length:

if len(df) == 0:
    # do something

Edit: the comments lead me to believe that your order of operations is wrong here.

def test(df = None):
    if not isinstance(df, pd.DataFrame):
        pass # do whatever
    elif df.empty:
        pass # do whatever else

None has no length, so len() throws an error, while df.empty will throw an error if df is None as well. Simply check if df is a DatFrame first, this will take care of the None values.