CODEWITHSUNDEEP
pythonstringpython-3.xformattingescaping
AKarpun
AKarpun

Reputation: 331

python 3.2.3 ignore escape sequence in string

I'm new to Python and I'm using one of the examples I found here to read lines from a file and print them. What I don't understand is why the interpreter ignores \n escape sequence:

Text file:

Which of the following are components you might find inside a PC? (Select all correct answers.)

A. CPU

B. Motherboard

C. Keyboard

Answers: A, B, and E. \nCommon components inside a PC include \nthe CPU,motherboard, and \nRAM

Python code:

questions_fname="Test.txt"

with open(questions_fname, 'r') as f:
    questions = [line.strip() for line in f]

for line in questions:
    print (line)


f.close()

The result I get is strings like:

Answers: A, B, and E. \nCommon components inside a PC include \nthe CPU,motherboard, and \nRAM

I was just looking for a simple way of formatting long lines to fit the screen.

Upvotes: 1

Views: 11707

Answers (4)

Bob
Bob

Reputation: 133

\ is an escape character only in Python script, not in text files. When reading text files, Python converts all backslashes to \\, so when reading the file, \n becomes \\n which is not a newline character

Upvotes: 0

pepr
pepr

Reputation: 20744

Try the following code to get the wanted behaviour...

questions_fname = "Test.txt"

with open(questions_fname) as f:
    for line in f:
        line = line.rstrip().replace('\\n', '\n')
        print(line)

The .rstrip() removes the trailing whitespaces, including the binary form of \n. The .replace() causes explicit, user defined interpretation of your \n sequences in the file content -- captured as the printable character \ followed by the n.

When using the with construct, the f.close() is done automatically.

Upvotes: 0

Jon Clements
Jon Clements

Reputation: 142106

Sorry - this isn't valid for Python 3.x (I was looking at the tags), but I'll leave here as reference - please see @Ignacio's answer: https://stackoverflow.com/a/14193673/1252759

If you've effectively got a raw string that contains the literal characters '\n', then you can re-interpret the string to make it an escape sequence again:

>>> a = r"Answers: A, B, and E. \nCommon components inside a PC include \nthe CPU,motherboard, and \nRAM"
>>> print a
Answers: A, B, and E. \nCommon components inside a PC include \nthe CPU,motherboard, and \nRAM
>>> print a.decode('string_escape')
Answers: A, B, and E. 
Common components inside a PC include 
the CPU,motherboard, and 
RAM

You may also want to look at the textwrap module if you want to wrap lines to a certain width for certain displays...

Upvotes: -1

Ignacio Vazquez-Abrams
Ignacio Vazquez-Abrams

Reputation: 798456

You don't have "\n" in the string, you have "\\n" since you're reading it from a file. If you want to have "\n" then you need to decode the string. Note that 3.x doesn't have str.decode(), so you can't use that mechanism from 2.x.

3>> codecs.getdecoder('unicode-escape')('foo\\nbar')[0]
'foo\nbar'

Upvotes: 4

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