Explicit line joining in Python

I am reading a file, line-by-line and doing some text processing in order to get output in a certain format My string processing code goes as follows:

file1=ope开发者_JS百科n('/myfolder/testfile.txt')
scanlines=file1.readlines()
string = ''

 for line in scanlines:
    if line.startswith('>from'):
         continue
    if line.startswith('*'):
        continue
    string.join(line.rstrip('\n')) 

The output of this code is as follows:

abc

def

ghi

Is there a way to join these physical lines into one logical line, e.g:

abcdefghi

Basically, how can I concatenate multiple strings into one large string?

If I was reading from a file with very long strings is there the risk of an overflow by concatenating multiple physical lines into one logical line?

there are several ways to do this. for example just using + should do the trick.

"abc" + "def" # produces "abcdef"

If you try to concatenate multiple strings you can do this with the join method:

', '.join(('abc', 'def', 'ghi')) # produces 'abc, def, ghi'

If you want no delimiter, use the empty string ''.join() method.

Cleaning things up a bit, it would be easiest to append to array and then return the result

def joinfile(filename) :
   sarray = []
   with open(filename) as fd :
       for line in fd :
           if line.startswith('>from') or line.startswith('*'):
               continue
          sarray.append(line.rstrip('\n'))
   return ''.join(sarray)

If you wanted to get really cute you could also do the following:

fd = open(filename)
str = ''.join([line.rstrip('\n') for line in fd if not (line.startswith('>from') or line.startswith('*'))])

Yes of course you could read a file big enough to overflow memory.

Use string addition

>>> s = 'a'
>>> s += 'b'
>>> s
'ab'

I would prefer:

oneLine = reduce(lambda x,y: x+y, \
                 [line[:-1] for line in open('/myfolder/testfile.txt') 
                            if not line.startswith('>from') and \
                               not line.startswith('*')])

• line[:-1] in order to remove all the \n
• the second argument of reduce is a list comprehension which extracts all the lines you are interested in and removes the \n from the lines.
• the reduce (just if you actually need that) to make one string from the list of strings.