Why is this basic python program not working?

Question

Well the program is supposed to check if the it sees an "ok" next to the email and if it does spit out the email in another txt file.

Input txt file:

.......ng0@gmail.com,ok
.......ad@live.com,fail
.......12@live.com,fail
.......5w@live.com,fail
.......np@gmail.com,ok
.......an@live.com,fail
.......40@excite.com,fail
.......g1@gmail.com,ok

python code is:

readEmails = open("C:\\Users\\Greg\\Desktop\\rewriteEmails.txt","r")
writeEmails = open("C:\\Users\\Greg\\Desktop\\OutputEmails.txt","w")

for line in readEmails:
    subbed = line[-3:]
    if subbed == "ok":
        split = line.split(",")
        writeEmails.write(split[0])
        print("Email Added")
    else:
        print("Error")

The program seems to always go to the else part of the if statement. I'm kinda having a brain fart; i would love your advice.

Have you done any basic debugging? If it seems to keep hitting the else condition, it means `subbed` is not `==` to "ok", so what is `line[-3:]` returning? — Sterling Archer, Jun 02 '15 at 15:48
If this is an actual csv file then consider using the [csv module](https://docs.python.org/2/library/csv.html), it will take care of the newlines and will split the fields for you. — Ashwini Chaudhary, Jun 02 '15 at 16:14

score 5 · Answer 1 · answered Jun 02 '15 at 15:48

5

This line: subbed = line[-3:] will give you the last 3 chars of line which can never be 'ok' which is 2 chars.

answered Jun 02 '15 at 15:48

Will

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rigel · Answer 2 · 2015-06-02T15:57:37.280

2

Instead of depending on string length (you have 3 instead of 2), you can do this line.strip().endswith('ok')

edited Jun 02 '15 at 15:57

answered Jun 02 '15 at 15:53

rigel

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This makes the intent of the code far clearer. Good suggestion. – wonderb0lt Jun 02 '15 at 15:58

doctorlove · Answer 3 · 2015-06-02T16:02:20.070

Simply that the last three characters of an "ok" line are ",ok":

>>> line = ".......g1@gmail.com,ok"
>>> line[-3:]
',ok'

edit The previous lines end in a new line, so we get the newline character included instead of the comma:

>>> line = """.......ng0@gmail.com,ok
... """
>>> line[-3:]
'ok\n'

edit ends

Perhaps you should just compare the last two characters:

for line in readEmails:
    subbed = line[-2:]
    #as you were

For a genuine error case, it is often reporting the error, then you can tell what's up easily. Instead of just saying

else:
    print("Error")

you could print out the subbed variable too, and it may have become obvious where the problem lay.

http://stackoverflow.com/questions/30600701/why-is-this-basic-python-program-not-working#comment49270188_30600778 — Ashwini Chaudhary, Jun 02 '15 at 15:56

Andy · Accepted Answer · 2015-06-02T16:17:27.260

1

Your problem is this line

subbed = line[-3:]

This returns the following:

ok\n

or

il\n

Thus, your if statement checking if subbed == 'ok' will fail every time.

You can fix this by only taking the last two characters, after stripping the newline:

subbed = line.strip()[-2:]

My original answer didn't account for reading from a file. That answer assumed that the results would be either ,ok or ail. This is not the correct response when reading from a file. The answer above has been modified to show what will be returned and adjusts the solution appropriately.

edited Jun 02 '15 at 16:17

answered Jun 02 '15 at 15:50

Andy

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`line[-3:]` will actually return `"ok\n"` or `'il\n'` apart from the last line. – Ashwini Chaudhary Jun 02 '15 at 15:54
For last line this may still fail though, it will be better to strip first and then take a slice of 2. – Ashwini Chaudhary Jun 02 '15 at 16:12
You are correct @AshwiniChaudhary. I've adjusted where the `strip()` occurs. – Andy Jun 02 '15 at 16:17

Aleksander Monk · Answer 5 · 2015-06-02T16:13:58.683

1

You can solve your problem with regex. Here is example for your code.

import re

for line in readEmails:
    subbed = re.match("(?:.*),(\\w+)", line)
    print(subbed.group(1))
    if subbed.group(1) == "ok":
        writeEmails.write(subbed.group(1))
        print("Email Added")
    else:
        print("Error")

edited Jun 02 '15 at 16:13

answered Jun 02 '15 at 15:59

Aleksander Monk

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@AshwiniChaudhary everything is better with regex. plus, in the future it will be very easy to change ending from "ok" to something else – Aleksander Monk Jun 02 '15 at 16:02
Regex is unnecessary for this trivial case, I would go for: `line.rstrip().endswith("ok")`. – Ashwini Chaudhary Jun 02 '15 at 16:12

Why is this basic python program not working?

5 Answers5