Why does Python 2.7.3 think my .csv document is all on one line?

Question

I'm new to programming and I encountered a problem in some of my coursework that I can't make any sense of. Consider an imaginary file called 'example.csv' with the following contents.

Key1,Value1
Key2,Value2
Key3,Value3
...

If I run the following code, it prints every line in the file followed by a single asterisk on the last line. I expected it to print each line separated by an asterisk.

infile = open("example.csv", "r")
for line in infile:
    print line.strip()
    print '*'
    #row_elements = line.split(",")
    #print row_elements

Furthermore, if I try to split the line at each comma by removing the hashes in the above code I get the following output.

['Key1', 'Value1\rKey2', 'Value2\rKey3'...

By instead passing "\r" to the .split() method the output is slightly improved.

['Key1,Value1', 'Key2,Value2'...

I still don't understand why python thinks the entire file is all on one line in the first place. Does anyone have insight into this?

Solution 1

Your file is using \r as line separators (also known as the "CR" or "Classic Mac" newline convention). Python's open doesn't deal with this by default.

You can use "universal newlines" mode ('rU' mode in open) to open the file properly.

(Note that some Mac text editors still use \r as the line terminator, though these are thankfully much less common now than they were a few years ago.)

Solution 2

Your input file is poorly formatted. On Linux, lines are separated by '\n'. On Windows, lines are separated by '\r\n', but code in the runtime library makes the '\r' disappear.

In your file, the lines are separated by '\r', which is not a standard in any modern operating system. Perhaps the program that created the file is flawed in some way.

Solution 3

if you're dealing with csv you should use the csv module, it takes care of most of the crap involved with processing csv input/output.

import csv
with open("example.csv", "rb") as infile:
    reader = csv.reader(infile)
    for row in reader:
        print row # a list of items in your file

The with statement hear will automatically close the file for you when you drop out of the statement block.

Comments

[matth]

True, but it doesn't answer his question nor solve his problem. He still needs to open with "U". Perhaps your answer would be better as a comment.

[Jeremy Caron]

This was very helpful and 'rU' mode worked just fine. Thanks!

[Jeremy Caron]

As I mentioned in the comments on the question, the culprit was Excel for Mac 2011. Thanks for the help.