user248237dfsf user248237dfsf - 4 months ago 11
Python Question

creating stream to iterate over from string in Python

I want to create a stream from a string in Python so that it's equivalent to reading the string as if it's read from a text file. something like:

for line in open('myfile.txt'): print line


except the contents of 'myfile.txt' are stored in a string
s
. Is this the correct/best way to do it?

s = StringIO.StringIO("a\t\b\nc\td\n")
for line in s: print line

Answer

I want to create a stream from a string in Python so that it's equivalent to reading the string as if it's read from a text file.

Is this the correct/best way to do it?

Yes, unless you really do want it in a list.

If it is intended to be consumed line by line, the way you are doing it makes sense.

StringIO() creates a file-like object.

File objects have a method, .readlines(), which materialize the object as a list. Instead of materializing the data in a list, you can iterate over it, which is more memory light:

# from StringIO import StringIO # Python 2 import
from io import StringIO # Python 3 import

txt = "foo\nbar\nbaz"

Here we append each line into a list, so that we can demonstrate iterating over the file-like object and keeping a handle on the data. (More efficient would be list(file_like_io).

m_1 = []
file_like_io = StringIO(txt)
for line in file_like_io:
    m_1.append(line)

and now:

>>> m_1
['foo\n', 'bar\n', 'baz']

you can return your io to any index point with seek:

>>> file_like_io.seek(0)
>>> file_like_io.tell() #print where we are in the object now
0

If you really want it in a list

.readlines() materializes the StringIO iterator as if one did list(io) - this is considered less preferable.

>>> m_2 = file_like_io.readlines() 

And we can see that our results are the same:

>>> m_1==m_2
True

Keep in mind that it is splitting after the newlines, preserving them in the text as well, so you'll get two newlines for every printed line, double-spacing on print.