'has_header from csv.Sniffer error: Could not determine delimiter'

Question

I want to check for an existing header in a newly created csv-file with the csv.Sniffer(). But I always get the same error:

:_csv.Error: Could not determine delimiter

The Code:

import csv

with open('example.csv', 'w') as csvfile:
    print("file created")

with open('example.csv', 'r') as check_header_file:
            has_header = csv.Sniffer().has_header(check_header_file.read(1024))

I've already tried to increase the size from 1024 to 2048 and to 3072.And I i tried to open the csv in 'rb' mode instead of only 'r'. For those who are interestet in the complete Traceback Call:

Traceback (most recent call last):
  File "c:/Users/USER/Documents/Hobby/Test.py", line 6, in <module>
    has_header = csv.Sniffer().has_header(check_header_file.read(1024))
  File "C:\Users\USER\AppData\Local\Programs\Python\Python38\lib\csv.py", line 393, in has_header
    rdr = reader(StringIO(sample), self.sniff(sample))
  File "C:\Users\USER\AppData\Local\Programs\Python\Python38\lib\csv.py", line 187, in sniff
    raise Error("Could not determine delimiter")
_csv.Error: Could not determine delimiter

And some pictures of the empty .csv where I'm trying to read the headers from

used csv-file in excel

used csv-file in VSCode

there is no previous file. The file is created in line 3 with: open('example-csv') — TheOneEmployee, Sep 04 '21 at 15:29
Both those images show empty files, so what exactly are you expecting the header or delimiter to be?? — OneCricketeer, Sep 04 '21 at 17:15
I expected that the function: csv.Sniffer().has_header returns false, because there is no header. — TheOneEmployee, Sep 04 '21 at 17:21
It doesn't. If you want to see if a file is empty, see https://stackoverflow.com/questions/2507808/how-to-check-whether-a-file-is-empty-or-not — OneCricketeer, Sep 04 '21 at 23:01
Thanks! It helped out a lot and cleared some misunderstandings I had. I managed to get the desired behaviour via try and exept without relying on the os library. I will post my solution as an answer later. — TheOneEmployee, Sep 05 '21 at 19:06

TheOneEmployee · Answer 1 · 2021-09-06T14:59:34.710

You can't check an empty .csv file with the python csv Sniffer. So I Tried a different approach with try and except. My Solution:

import csv

#array of Headers
fields = ['Header1', 'Header2', 'Header3'] 

#if .csv file doesn't exist, create one
#try to read from desired file, to check if one exists
try:
    with open('example.csv', 'r', newline='') as csvfile: 
        print('file exists')
#if desired file doesn't exist, create it with the write ('w') or 
#append 'a' mode
except:
    with open('example.csv', 'a', newline='') as csvfile: 
        print('file created')

#if .csv file doesn't contain Headers, populate it with Headers
#read first row in file, to check if some Headers exists 
with open('example.csv', 'r') as csvfile:
    try:
        reader = csv.reader(csvfile)
        row1 = next(reader)
        print("headers exist")
        print(row1)
#if no Headers exists, create Headers with the help of the 
#previously declared and initialized fields array
    except:
        with open('example.csv', 'w', encoding='UTF8', newline='') as csvfile: 
            writer = csv.DictWriter(csvfile, fieldnames = fields) 
            writer.writeheader()
            print("write headers")

First you check with try if a file already exists or has Headers. And in except will the file or the Header created, if none exists

Please provide additional details in your answer. As it's currently written, it's hard to understand your solution. — Community, Sep 05 '21 at 19:58
I don't really like to use an extra library for a problem that can be solved without it. And i had some problems in the past to check for a file through a specific path — TheOneEmployee, Sep 06 '21 at 14:52
`os` and `csv` are part of the Standard library, there is no "cost" to import them. Using try-except statements is actually slower than checking directly for file existence or sizes — OneCricketeer, Sep 06 '21 at 15:07

'has_header from csv.Sniffer error: Could not determine delimiter'

1 Answers1