Overwriting an existing txt file with new data using Python OS module

Question

I am following the code mentioned by SO User "qmorgan" here, basically I am trying to create new text file if file doesn't exist. If file exist then overwrite the existing file. For this my code looks like below. The issue I am facing is using 'a' for writing the file it is append the text instead of overwriting it. As 'a' function is to append the text under first if condition. If I use "W" instead of "a" then it would only write last record, instead of all the records.

Thanks in advance for help and efforts!

Python code

filename='test.txt'
  
tables=["schema.table1","schema2.table2"]
    
for table in tables:
   cur.execute (f'select count(*) from {table};')
   result=cur.fecthone()
   count=result[0] if result else 0
   for row in result:
       if os.path.exists(filename):
            append_write='a'
            my_file.close()
       else:
          append_write='w+'
       my_file=open(filename,append_write)
       my_file.write(f"the table {table} contained {count} rows. \n")
       my_file.close()

What is `o`? Is that supposed to be `0`? There's no need for that `if`, since `SELECT COUNT(*)` will *always* return a row. — Barmar, May 20 '22 at 15:19
Open the file *once* at the top. Then write to it in a loop. — juanpa.arrivillaga, May 20 '22 at 15:19
Before the `for table in tables:` command. If you do it this way, you don't need to use `os.path.exists()`. Just use `w` mode and it will always overwrite the file. — Barmar, May 20 '22 at 15:35

score 1 · Accepted Answer · answered May 20 '22 at 15:41

1

Just open the file once at the beginning, not separately for each query. Then you can simply use w mode to overwrite it.

There's also no need for the for row in result: loop, since you never use row anywhere. result is a tuple with just a single element, the count returned by COUNT(*), there's nothing else to loop over.

filename='test.txt'
  
tables=["schema.table1","schema2.table2"]
    
with open(filename, 'w') as my_file:
    for table in tables:
        cur.execute(f'select count(*) from {table};')
        (count,) = cur.fetchone()
        my_file.write(f"the table {table} contained {count} rows. \n")

answered May 20 '22 at 15:41

Barmar

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Thank you it worked! Was wondering if I need to close my_file.close() ? – biggboss2019 May 20 '22 at 15:46
1

Why? Don't you know that `with` does that automatically? It's the whole point of using `with`. – Barmar May 20 '22 at 15:48

Overwriting an existing txt file with new data using Python OS module

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