How to make if statement on empty list in python

Question

I have a small problem with creating an if statement in python. I am compering two csv files using Panda Library and I want to create an if statement which will be checking if list is empty. So this is my code

file1 = pd.read_csv('otomotofirst.csv')
file2 = pd.read_csv('otomotonew.csv')

change=(file2[~file2.Linki.isin(file1.Linki)])

if change is None:
    break
else:
    send_mail(subjectNew,change)

It is working quite well, however if it is empty (or in my case None) email is also sent. Of course it sends an empty list but it doesn't break.

I was trying do it with True and False statement but this error always pop ups

ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all()

A dataframe behaves differently from a list when it comes to truthiness and falsiness. You can use change.shape[0] or len(change) to check if the length is 0 — G. Anderson
– G. Anderson, Commented Apr 16, 2020 at 17:17

ALollz · Accepted Answer · 2020-04-16 17:26:09Z

2

You don't have a list, you have a DataFrame. DataFrames, even empty, are not None.

pd.DataFrame() is None
False

You check if a DataFrame is empty with the empty attribute.

pd.DataFrame().empty
True

Regarding the error, you can't treat a DataFrame like a list to check emptiness

if []: print(True)              # Works 
if pd.DataFrame(): print(True)  # ValueError

The code should be

if change.empty:
    break
else:
    send_mail(subjectNew, change)

answered Apr 16, 2020 at 17:26

ALollz

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Comments

Diogo Lopes · Accepted Answer · 2020-04-16 17:29:11Z

0

You may use os.path.getsize() in order to obtain the size of a file. So, if you wnat to check if your file is empty:

filesize = os.path.getsize("file.csv")
filesize1 = os.path.getsize("file1.csv")

def file_compare():
  if(filesize == 0 and filesize == 0):
      print("Both files are empty")
  if(filesize == filesize1):
      print("File sizes are equal", str(filesize)
  else:
      print(str(filesize))
      print(str(filesize1))`

Hope it works!

answered Apr 16, 2020 at 17:29

Diogo Lopes

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1 Comment

Mateusz Broncel Over a year ago

It is not what I was looking for but still thank you very much

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