Python readline() 来自字符串？

Question

In python, is there a built-in way to do a readline() on string? I have a large chunk of data and want to strip off just the first couple lines w/o doing split() on the whole string.

Hypothetical example:

def handleMessage(msg):
   headerTo  = msg.readline()
   headerFrom= msg.readline()
   sendMessage(headerTo,headerFrom,msg)

msg = "Bob Smith\nJane Doe\nJane,\nPlease order more widgets\nThanks,\nBob\n"
handleMessage(msg)

I want this to result in: sendMessage("Bob Smith", "Jane Doe", "Jane,\\nPlease order...")

I know it would be fairly easy to write a class that does this, but I'm looking for something built-in if possible.

EDIT: Python v2.7

Answer 1

In Python 3, you can use io.StringIO :

>>> msg = "Bob Smith\nJane Doe\nJane,\nPlease order more widgets\nThanks,\nBob\n"
>>> msg
'Bob Smith\nJane Doe\nJane,\nPlease order more widgets\nThanks,\nBob\n'
>>>
>>> import io
>>> buf = io.StringIO(msg)
>>> buf.readline()
'Bob Smith\n'
>>> buf.readline()
'Jane Doe\n'
>>> len(buf.read())
44

---

In Python 2, you can use StringIO (orcStringIO if performance is important):

>>> import StringIO
>>> buf = StringIO.StringIO(msg)
>>> buf.readline()
'Bob Smith\n'
>>> buf.readline()
'Jane Doe\n'

Answer 2

The easiest way for both python 2 and 3 is using string's method splitlines (). This returns a list of lines.

>>> "some\nmultilene\nstring\n".splitlines()

['some', 'multilene', 'string']

Answer 3

Why not just only do as many splits as you need? Since you're using all of the resulting parts (including the rest of the string), loading it into some other buffer object and then reading it back out again is probably going to be slower, not faster (plus the overhead of function calls).

If you want the first N lines separated out, just do .split("\\n", N) .

>>> foo = "ABC\nDEF\nGHI\nJKL"
>>> foo.split("\n", 1)
['ABC', 'DEF\nGHI\nJKL']
>>> foo.split("\n", 2)
['ABC', 'DEF', 'GHI\nJKL']

So for your function:

def handleMessage(msg):
   headerTo, headerFrom, msg = msg.split("\n", 2)
   sendMessage(headerTo,headerFrom,msg)

or if you really wanted to get fancy:

# either...
def handleMessage(msg):
   sendMessage(*msg.split("\n", 2))

# or just...
handleMessage = lambda msg: sendMessage(*msg.split("\n", 2))

Answer 4

Do it like StringIO does it:

i = self.buf.find('\n', self.pos)

So this means:

pos = msg.find("\n")
first_line = msg[:pos]
...

Seems more elegant than using the whole StringIO...

Answer 5

in Python string have method splitlines

msg = "Bob Smith\nJane Doe\nJane,\nPlease order more widgets\nThanks,\nBob\n"
msg_splitlines = msg.splitlines()
headerTo = msg_splitlines[0]
headerFrom= msg_splitlines[1]
sendMessage(headerTo,headerFrom,msg)