How do I split a multi-line string into multiple lines?

Question

I have a multi-line string that I want to do an operation on each line, like so:

inputString = """Line 1
Line 2
Line 3"""

I want to iterate on each line:

for line in inputString:
    doStuff()

Answer 1

inputString.splitlines()

Will give you a list with each item, the splitlines() method is designed to split each line into a list element.

Answer 2

inputString.split('\n')  # --> ['Line 1', 'Line 2', 'Line 3']

This is identical to the above, but the string module's functions are deprecated and should be avoided:

import string
string.split(inputString, '\n')  # --> ['Line 1', 'Line 2', 'Line 3']

Alternatively, if you want each line to include the break sequence (CR,LF,CRLF), use the splitlines method with a True argument:

inputString.splitlines(True)  # --> ['Line 1\n', 'Line 2\n', 'Line 3']

Answer 3

Use inputString.splitlines().

---

Why splitlines is better

splitlines handles newlines properly, unlike split.

It also can optionally return the newline character in the split result when called with a True argument, which is useful in some specific scenarios.

---

Why you should NOT use split("\n")

Using split creates very confusing bugs when sharing files across operating systems.

\n in Python represents a Unix line-break (ASCII decimal code 10), independently of the OS where you run it. However, the ASCII linebreak representation is OS-dependent.

On Windows, \n is two characters, CR and LF (ASCII decimal codes 13 and 10, \r and \n), while on modern Unix (Mac OS X, Linux, Android), it's the single character LF.

print works correctly even if you have a string with line endings that don't match your platform:

>>> print " a \n b \r\n c "
 a 
 b 
 c

However, explicitly splitting on "\n", has OS-dependent behaviour:

>>> " a \n b \r\n c ".split("\n")
[' a ', ' b \r', ' c ']

Even if you use os.linesep, it will only split according to the newline separator on your platform, and will fail if you're processing text created in other platforms, or with a bare \n:

>>> " a \n b \r\n c ".split(os.linesep)
[' a \n b ', ' c ']

splitlines solves all these problems:

>>> " a \n b \r\n c ".splitlines()
[' a ', ' b ', ' c ']

---

Reading files in text mode partially mitigates the newline representation problem, as it converts Python's \n into the platform's newline representation.

However, text mode only exists on Windows. On Unix systems, all files are opened in binary mode, so using split('\n') in a UNIX system with a Windows file will lead to undesired behavior. This can also happen when transferring files in the network.

Answer 4

Might be overkill in this particular case but another option involves using StringIO to create a file-like object

for line in StringIO.StringIO(inputString):
    doStuff()

Answer 5

I would like to augment @1_CR 's answer: He led me to the following technique; it will use cStringIO if available (BUT NOTE: cStringIO and StringIO are not the same, because you cannot subclass cStringIO... it is a built-in... but for basic operations the syntax will be identical, so you can do this):

try:
    import cStringIO
    StringIO = cStringIO
except ImportError:
    import StringIO

for line in StringIO.StringIO(variable_with_multiline_string):
    pass
print line.strip()

Answer 6

The original post requested for code which prints some rows (if they are true for some condition) plus the following row. My implementation would be this:

text = """1 sfasdf
asdfasdf
2 sfasdf
asdfgadfg
1 asfasdf
sdfasdgf
"""

text = text.splitlines()
rows_to_print = {}

for line in range(len(text)):
    if text[line][0] == '1':
        rows_to_print = rows_to_print | {line, line + 1}

rows_to_print = sorted(list(rows_to_print))

for i in rows_to_print:
    print(text[i])

Answer 7

in Python3 use this code

from io import StringIO
for sline in sio.readlines():
        print(sline)