CODEWITHSUNDEEP
pythonpython-3.x
vPilot
vPilot

Reputation: 48

Avoiding multiple open/closes of file in Python

I have written my first Python script (yay) for performing a query against a Postgres database to: count the number of rows in a table, delete rows from that table based on date criteria, then count rows again to show that the deletion was indeed successful. For each of those portions, a file is opened, updated, and closed to record each task as it's completed.

A comment by a peer, however, has made me wonder if there's a better way to handle writes to the file instead of opening and closing it at each task. He made mention of python's logging library, but in my inexperience I feel like I may be missing it's utility as it relates to what could improve writing to file.

Here's a snippet of the script showing what I'm doing presently:

cur = con.cursor()
cur.execute("SELECT COUNT(*) OVER() FROM test LIMIT 1")
rows = cur.fetchall()

for row in rows:
    logFile = open('/var/log/test_script.log', 'a')
    print("Pre-Delete Row Count =", row[0], file = logFile)
    logFile.close()

Thoughts about how writing to file could be improved based on the snippet?

Upvotes: 1

Views: 61

Answers (2)

gordon so
gordon so

Reputation: 309

Firstly, you can use the context manager syntax for file, secondly, you can put the open context outside of the for loop; see example:

cur = con.cursor()
cur.execute("SELECT COUNT(*) OVER() FROM test LIMIT 1")
rows = cur.fetchall()

with open('/var/log/test_script.log', 'a') as f:
    for row in rows:
        print("Pre-Delete Row Count =", row[0], file = f)

Upvotes: 1

L3viathan
L3viathan

Reputation: 27283

You can just move the opening of the file above the for loop:

cur = con.cursor()
cur.execute("SELECT COUNT(*) OVER() FROM test LIMIT 1")
rows = cur.fetchall()

with open('/var/log/test_script.log', 'a') as logFile:
    for row in rows:
        print("Pre-Delete Row Count =", row[0], file=logFile)

Note that you no longer need to close the file when using it as a context manager.

Upvotes: 1

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