Question

We need to display some “preview text” from a larger string that can be, at most, ‘n’ characters long. Unfortunately, I couldn’t find an existing module on PyPi that handles this.

I’m hoping to do a proper solution. While my quick & dirty solution below works, it’s not that efficient — lots of constant comparisons. Does anyone have an idea on how to improve? I tried a regex, but gave up after 20 minutes.

The kludgy solution I came up with is good enough for most needs, I just know this could be done faster and more concisely – and I’d love to know how.

sample = "This is a sample string and I would like to break it down by words, without exceeding max_chars."

def clean_cut( text , max_chars ):
    rval = []
    words = text.split(' ')
    for word in words:
        len_rval = len(' '.join(rval))
        if len_rval + 1 + len(word) > max_chars :
            break
        rval.append(word)
    return ' '.join(rval)

for i in ( 15, 16, 17,30,35):
    cutdown = clean_cut( sample , i )
    print "%s | %s" % ( i , cutdown )

and output is right…

15 | This is a
16 | This is a sample
17 | This is a sample
30 | This is a sample string and I
35 | This is a sample string and I would

Answer 1

The following implementation may work for you

def clean_cut(st, end):
    st += ' ' #In case end > len(st)
    return st[:st[:end + 1].rfind(' ')]
for i in ( 15, 16, 17,30,35):
    cutdown = clean_cut( sample , i )
    print "%s | %s" % ( i , cutdown )

Output

15 | This is a
16 | This is a sample
17 | This is a sample
30 | This is a sample string and I
35 | This is a sample string and I would

---

Note

Compared to textwrap, this implementation is 50 times faster

>>> stmt_ab = """
for i in ( 15, 16, 17,30,35):
    cutdown = sample[:sample[:i + 1].rfind(' ')]
"""
>>> stmt_mg = """
for i in ( 15, 16, 17,30,35):
    cutdown =  textwrap.wrap(sample[:i+1],i)[0]
"""
>>> import timeit
>>> t1_ab = timeit.Timer(stmt=stmt_ab, setup = "from __main__ import sample")
>>> t1_mg = timeit.Timer(stmt=stmt_mg, setup = "from __main__ import sample, textwrap")
>>> t1_ab.timeit(10000)
0.10367805429780219
>>> t1_mg.timeit(10000)
5.597085870104877
>>>