Маймон, ваш исходный код неверен в отношении индексов. И код Эндрю тоже неверен, потому что он принял ваш код за начало.
См. Результат кода Эндрю, в котором я исключил строки, касающиеся g :
import sys
import operator
import linecache
x=0
y=7 # to skip
z=3 # to print
#g = open('tmp','a+')
while x<23:
x+=1
print 'x==',x
if operator.mod(x, y)==0:
#curr = g.tell()
for i in range(x,x+z):
block=linecache.getline('poem.txt', i)
print 'block==',repr(block)
#g.write(block)
linecache.clearcache()
#g.seek(curr)
#lines = g.read()
#find(lines)
else:
pass
#g.close()
применяется к файлу с именем 'poem.txt', содержащему 24 строки:
1 In such a night, when every louder wind
2 Is to its distant cavern safe confined;
3 And only gentle Zephyr fans his wings,
4 And lonely Philomel, still waking, sings;
5 Or from some tree, famed for the owl's delight,
6 She, hollowing clear, directs the wand'rer right:
7 In such a night, when passing clouds give place,
8 Or thinly veil the heav'ns' mysterious face;
9 When in some river, overhung with green,
10 The waving moon and trembling leaves are seen;
11 When freshened grass now bears itself upright,
12 And makes cool banks to pleasing rest invite,
13 Whence springs the woodbind, and the bramble-rose,
14 And where the sleepy cowslip sheltered grows;
15 Whilst now a paler hue the foxglove takes,
16 Yet checkers still with red the dusky brakes
17 When scattered glow-worms, but in twilight fine,
18 Shew trivial beauties watch their hour to shine;
19 Whilst Salisb'ry stands the test of every light,
20 In perfect charms, and perfect virtue bright:
21 When odors, which declined repelling day,
22 Through temp'rate air uninterrupted stray;
23 When darkened groves their softest shadows wear,
24 And falling waters we distinctly hear;
Результат:
x== 1
x== 2
x== 3
x== 4
x== 5
x== 6
x== 7
block== '7 In such a night, when passing clouds give place,\n'
block== "8 Or thinly veil the heav'ns' mysterious face;\n"
block== '9 When in some river, overhung with green,\n'
x== 8
x== 9
x== 10
x== 11
x== 12
x== 13
x== 14
block== '14 And where the sleepy cowslip sheltered grows;\n'
block== '15 Whilst now a paler hue the foxglove takes,\n'
block== '16 Yet checkers still with red the dusky brakes\n'
x== 15
x== 16
x== 17
x== 18
x== 19
x== 20
x== 21
block== '21 When odors, which declined repelling day,\n'
block== "22 Through temp'rate air uninterrupted stray;\n"
block== '23 When darkened groves their softest shadows wear,\n'
x== 22
x== 23
x== 24
x== 25
Я выбрал y = 7 для количества пропускаемых строк, но строка 7 печатается.
Кроме того, отсчет продолжается с 8, 9, 10 ... после того, как вы напечатали 3 строки 7-8-9 (выбрав z = 3) вместо продолжения с 10, 11, 12 ... Затем следующий 3 строки напечатаны 14-15-16, в то время как это должны быть строки после 7 + 3 первых строк, то есть строки 11-12-13
На самом деле, если вы хотите пропустить 7 строк, а затем напечатать 3 строки, напечатанные строки должны быть:
8-9-10
18-19-20
28-29-30
и т.д.
Я прав?
РЕДАКТИРОВАТЬ 1
Мое решение:
def chunk_reading(filepath,y,z,x=0):
# x : number of lines to skip before the periodical treatment
# y : number of lines to periodically skip
# z : number of lines to periodically print
with open('poem.txt') as f:
try:
for sk in xrange(x):
f.next()
while True:
try:
for i in xrange(y):
print 'i==',i
f.next()
for j in xrange(z):
print 'j==',j
print repr(f.next())
except StopIteration:
break
except StopIteration:
print 'Not enough lines before the lines to print'
chunk_reading('poem.txt',7,3)
производит:
i== 0
i== 1
i== 2
i== 3
i== 4
i== 5
i== 6
j== 0
"8 Or thinly veil the heav'ns' mysterious face;\n"
j== 1
'9 When in some river, overhung with green,\n'
j== 2
'10 The waving moon and trembling leaves are seen;\n'
i== 0
i== 1
i== 2
i== 3
i== 4
i== 5
i== 6
j== 0
'18 Shew trivial beauties watch their hour to shine;\n'
j== 1
"19 Whilst Salisb'ry stands the test of every light,\n"
j== 2
'20 In perfect charms, and perfect virtue bright:\n'
i== 0
i== 1
i== 2
i== 3
i== 4
РЕДАКТИРОВАТЬ 2
Приведенное выше решение применимо даже для очень больших файлов, которые невозможно записать в ОЗУ.
Следующий файл можно использовать для файлов ограниченного размера:
def slice_reading(filepath,y,z,x=0):
# x : number of lines to skip before the periodical treatment
# y : number of lines to periodically skip
# z : number of lines to periodically print
with open('poem.txt') as f:
lines = f.readlines()
lgth = len(lines)
if lgth > x+y:
for a in xrange(x+y,lgth,y+z):
print lines[a:a+z]
else:
print 'Not enough lines before lines to print'
slice_reading('poem.txt',7,3,5)
результат
['13 Whence springs the woodbind, and the bramble-rose,\n', '14 And where the sleepy cowslip sheltered grows;\n', '15 Whilst now a paler hue the foxglove takes,\n']
['23 When darkened groves their softest shadows wear,\n', '24 And falling waters we distinctly hear;']