Dan Liang wrote:
Hi Bob and tutors,
Thanks Bob for your response! currently I have the current code, but
it does not work:
[snip]
Thank you for code, sample data and more complete specs.
Lines in the file look like following:
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
word1 word2 word3 word4 yes
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 no
word1 word2 word3 word4 yes
Any suggestions are appreciated. Also, I feel that my code is not the
best way of solving the problem even if the problem of list indices is
solved. Is my guess right?
Yes indeed. In actuality you need only to examine one line at a time and
keep track of the "state" of things.
In computer theory we refer to a "state machine". There is a set of
states. The program is always in exactly one of these states. In each
state there are actions to take and a (conditional) moves to other states.
the program starts in, let's say, state 0:
state 0: open file, goto state 1.
state 1: read next line, at eof goto state 6; if it ends in yes, goto
state 2 else stay in state 1.
state 2: read next line, at eof goto state 6; if it ends in yes stay in
state 2 else goto state 3.
state 3: read next line, at eof goto state 6. if it ends in yes goto
state 2 else print line and goto state 4.
state 4: read next line, at eof goto state 6. if it ends in yes goto
state 2 else print line and goto state 5.
state 5: read next line, at eof goto state 6. if it ends in yes goto
state 2 else stay in state 5.
state 6: close file and terminate
That can be implemented in Python as follows. This is not the prettiest
or most compact program, but is it a straightforward implementation of a
state machine.
state = 0 # initial state
data = open('test.txt')
while True: # iterate over lines
if state == 0: # look for first line ending in 'yes'
line = data.read().strip()
if line:
if line.endswith('yes'):
state = 1
else state = 6
elif state == 1:
# code for state i
# more states
elif state == 6:
data.close()
break
To simplify things I'd create a function to read and strip a line and
raise an exception at end of file.
--
Bob Gailer
Chapel Hill NC
919-636-4239
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