[英]Special End-line characters/string from lines read from text file, using Python
我需要從文本文件中讀取行,但是其中“行尾”字符並不總是\\ n或\\ x或其組合,並且可以是諸如“ xyz”或“ |”之類的字符的任意組合,而是“ end”的“行”始終是相同的,並且對於每種類型的文件都是已知的。
由於文本文件可能很大,因此我必須牢記性能和內存使用情況,似乎最好的解決方案是什么? 今天,我使用string.read(1000)和split(myendofline)或partition(myendofline)的組合,但我知道是否存在更優雅,更標准的解決方案。
顯然,最簡單的方法是先閱讀整個內容,然后調用.split('|')
。
但是,如果這是不希望的,因為這需要您將整個內容讀取到內存中,則可以讀取任意塊並對其進行拆分。 您可以編寫一個類,該類在當前的一個塊用完時可以捕獲另一個任意塊,而您的應用程序的其余部分則不需要了解它。
這是輸入zen.txt
The Zen of Python, by Tim Peters||Beautiful is better than ugly.|Explicit is better than implicit.|Simple is better than complex.|Complex is better than complicated.|Flat is better than nested.|Sparse is better than dense.|Readability counts.|Special cases aren't special enough to break the rules.|Although practicality beats purity.|Errors should never pass silently.|Unless explicitly silenced.|In the face of ambiguity, refuse the temptation to guess.|There should be one-- and preferably only one --obvious way to do it.|Although that way may not be obvious at first unless you're Dutch.|Now is better than never.|Although never is often better than *right* now.|If the implementation is hard to explain, it's a bad idea.|If the implementation is easy to explain, it may be a good idea.|Namespaces are one honking great idea -- let's do more of those!
這是我的小測試用例,適用於我。 它不能處理很多角落的情況,也不是特別漂亮,但是應該可以幫助您入門。
class SpecialDelimiters(object):
def __init__(self, filehandle, terminator, chunksize=10):
self.file = filehandle
self.terminator = terminator
self.chunksize = chunksize
self.chunk = ''
self.lines = []
self.done = False
def __iter__(self):
return self
def next(self):
if self.done:
raise StopIteration
try:
return self.lines.pop(0)
except IndexError:
#The lines list is empty, so let's read some more!
while True:
#Looping so even if our chunksize is smaller than one line we get at least one chunk
newchunk = self.file.read(self.chunksize)
self.chunk += newchunk
rawlines = self.chunk.split(self.terminator)
if len(rawlines) > 1 or not newchunk:
#we want to keep going until we have at least one block
#or reached the end of the file
break
self.lines.extend(rawlines[:-1])
self.chunk = rawlines[-1]
try:
return self.lines.pop(0)
except IndexError:
#The end of the road, return last remaining stuff
self.done = True
return self.chunk
zenfh = open('zen.txt', 'rb')
zenBreaker = SpecialDelimiters(zenfh, '|')
for line in zenBreaker:
print line
這是一個生成器函數,它充當文件上的迭代器 ,根據所有文件中相同的奇異換行符剪切行。
它按大塊lenchunk
字符讀取文件,並在每個大塊中lenchunk
顯示行。
由於在我的示例中,換行符是3個字符(':;:'),所以可能會發生以下情況:大塊以剪切換行符結尾:此生成器函數負責這種可能性,並設法顯示正確的行。
如果換行符只是一個字符,則可以簡化功能。 我只為最微妙的情況編寫了函數。
使用此功能可以一次只讀取一行文件,而無需將整個文件讀取到內存中。
from random import randrange, choice
# this part is to create an exemple file with newline being :;:
alphabet = 'abcdefghijklmnopqrstuvwxyz '
ch = ':;:'.join(''.join(choice(alphabet) for nc in xrange(randrange(0,40)))
for i in xrange(50))
with open('fofo.txt','wb') as g:
g.write(ch)
# this generator function is an iterator for a file
# if nl receives an argument whose bool is True,
# the newlines :;: are returned in the lines
def liner(filename,eol,lenchunk,nl=0):
# nl = 0 or 1 acts as 0 or 1 in splitlines()
L = len(eol)
NL = len(eol) if nl else 0
with open(filename,'rb') as f:
chunk = f.read(lenchunk)
tail = ''
while chunk:
last = chunk.rfind(eol)
if last==-1:
kept = chunk
newtail = ''
else:
kept = chunk[0:last+L] # here: L
newtail = chunk[last+L:] # here: L
chunk = tail + kept
tail = newtail
x = y = 0
while y+1:
y = chunk.find(eol,x)
if y+1: yield chunk[x:y+NL] # here: NL
else: break
x = y+L # here: L
chunk = f.read(lenchunk)
yield tail
for line in liner('fofo.txt',':;:'):
print line
這是相同的,這里和那里的印刷允許遵循算法。
from random import randrange, choice
# this part is to create an exemple file with newline being :;:
alphabet = 'abcdefghijklmnopqrstuvwxyz '
ch = ':;:'.join(''.join(choice(alphabet) for nc in xrange(randrange(0,40)))
for i in xrange(50))
with open('fofo.txt','wb') as g:
g.write(ch)
# this generator function is an iterator for a file
# if nl receives an argument whose bool is True,
# the newlines :;: are returned in the lines
def liner(filename,eol,lenchunk,nl=0):
L = len(eol)
NL = len(eol) if nl else 0
with open(filename,'rb') as f:
ch = f.read()
the_end = '\n\nxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'+\
'\nend of the file=='+ch[-50:]+\
'\nxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx\n'
f.seek(0,0)
chunk = f.read(lenchunk)
tail = ''
while chunk:
if (chunk[-1]==':' and chunk[-3:]!=':;:') or chunk[-2:]==':;':
wr = [' ##########---------- cut newline cut ----------##########'+\
'\nchunk== '+chunk+\
'\n---------------------------------------------------']
else:
wr = ['chunk== '+chunk+\
'\n---------------------------------------------------']
last = chunk.rfind(eol)
if last==-1:
kept = chunk
newtail = ''
else:
kept = chunk[0:last+L] # here: L
newtail = chunk[last+L:] # here: L
wr.append('\nkept== '+kept+\
'\n---------------------------------------------------'+\
'\nnewtail== '+newtail)
chunk = tail + kept
tail = newtail
wr.append('\n---------------------------------------------------'+\
'\ntail + kept== '+chunk+\
'\n---------------------------------------------------')
print ''.join(wr)
x = y = 0
while y+1:
y = chunk.find(eol,x)
if y+1: yield chunk[x:y+NL] # here: NL
else: break
x = y+L # here: L
print '\n\n==================================================='
chunk = f.read(lenchunk)
yield tail
print the_end
for line in liner('fofo.txt',':;:',1):
print 'line== '+line
。
編輯
我比較了我的代碼和chmullig的代碼的執行時間。
使用約10 MB的“ fofo.txt”文件創建
alphabet = 'abcdefghijklmnopqrstuvwxyz '
ch = ':;:'.join(''.join(choice(alphabet) for nc in xrange(randrange(0,60)))
for i in xrange(324000))
with open('fofo.txt','wb') as g:
g.write(ch)
並像這樣測量時間:
te = clock()
for line in liner('fofo.txt',':;:', 65536):
pass
print clock()-te
fh = open('fofo.txt', 'rb')
zenBreaker = SpecialDelimiters(fh, ':;:', 65536)
te = clock()
for line in zenBreaker:
pass
print clock()-te
我在幾篇文章中獲得了以下最少時間:
............我的代碼0,7067秒
chmullig的代碼0.8373秒
。
編輯2
我更改了生成器函數: liner2()
接受文件處理程序而不是文件名。 因此,文件的打開可以不計入時間,因為它用於chmullig代碼的計測
def liner2(fh,eol,lenchunk,nl=0):
L = len(eol)
NL = len(eol) if nl else 0
chunk = fh.read(lenchunk)
tail = ''
while chunk:
last = chunk.rfind(eol)
if last==-1:
kept = chunk
newtail = ''
else:
kept = chunk[0:last+L] # here: L
newtail = chunk[last+L:] # here: L
chunk = tail + kept
tail = newtail
x = y = 0
while y+1:
y = chunk.find(eol,x)
if y+1: yield chunk[x:y+NL] # here: NL
else: break
x = y+L # here: L
chunk = fh.read(lenchunk)
yield tail
fh = open('fofo.txt', 'rb')
te = clock()
for line in liner2(fh,':;:', 65536):
pass
print clock()-te
經過大量文章以查看最短時間后的結果是
......... with線性()0.7067秒
....... with線性2()0.7064秒
chmullig的代碼0.8373秒
實際上,打開文件在整個時間中只占很小的一部分。
給定您的約束,最好先將已知的異常換行轉換為普通換行,然后再使用通常的換行:
for line in file:
...
TextFileData.split(EndOfLine_char)
似乎是您的解決方案。 如果運行速度不夠快,則應考慮使用較低級別的編程級別。
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