Midterm Exam 2 Review Fall 2003: Reverse a file
Answers? Comments? Questions on Answers? Questions on Comments?
(Back to Fall2003 Midterm Review 2)
"You are trying to access a part of the object that doesn't exist." error again at line "startingString":
| Again, because readlines() returns a list, and lists don't understand .find. Mark Guzdial |
def reverseFile(filename):
file = open(filename,"rt")
fileContents = file.readlines()
file.close()
reversedFile = open(filename,"wt")
for string in fileContents:
startingString = fileContents.find("\n",string)
endingString = fileContents.find("'",startingString - 1)
copyingString = fileContents[startingString-1:ending2String]
reversedFile.write(copyingString)
startingString = startingString - 1
reversedFile.close()
file = open(filename,"rt")
print file.read()
file.close()
| If you have all the lines in a list, and lists understand the method reverse(), why don't you just use that? Mark Guzdial |
i got it working but with the returns. do u want the return or get rid of the returns and if you do want to get rid of returns, how should i go about doing it :)
def reverseFile(filename):
file = open(filename,"rt")
fileContents = file.readlines()
file.close()
reverseContents = fileContents.reverse()
print fileContents
def reverseFile(filename):
file = open(getMediaPath(filename), "rt")
fileContents = file.readlines()
file.close()
reversed = open("reversed.txt","wt")
fileContents.reverse()
for line in fileContents:
reversed.write(line)
reversed.close()
fileedit = open("reversed.txt","rt")
print fileedit.read()
fileedit.close()
where i put print file.read() i get back the right thing, but i dont know how to make JES actually write this out into a txt called reversed. anybody have any ideas?
since the last line might not have the return '\n', it would mess up the output, I added this line to make sure it has the return at the end:
if (each[len(each)-1:len(each)] <> "\n"):
each = each + '\n'
if my variable "mylines"=the reverse of the file, how do I write it out to another file?
reverse=open("reverse.txt","wt")
reverse.write("mylines")
this doesnt work. it only writes "mylines" to the file. what am i doing wrong?
Try not putting it in quotes? You're making it a string instead of a variable.
| Perhaps try writing each line out separately? Use a loop? Mark Guzdial |
finally works.........writes out the revesed of the original to the original text file.
def reverseFile(filename):
file = open(filename,"rt")
fileContents = file.readlines()
file.close()
fileContents.reverse()
print fileContents
reversedFile = open(filename,"wt")
for item in fileContents:
reversedFile.write(item)
reversedFile.close()
reversedFile = open(filename,"rt")
fileContents = reversedFile.read()
reversedFile.close()
print fileContents
what does "rt" and "wt" do?
read text and write text maybe???
| "rt" means "read text". "wt" means "write text." Yup. Mark Guzdial |
When I tried the last suggestion in JES, I got
>>> reverseFile(file)
['file, okay?\n', 'ordinary\n', 'a perfectly\n', 'This is\n']
An error occurred attempting to pass an argument to a function.
Please check line 9 of C:\Documents and Settings\Dina Forehand\My Documents\JES\reverseFile.py
>>>
What happened?
| Diana, could you show us the program? What's on line 9? Mark Guzdial |
def reverseFile(filename):
file = open(filename,"rt")
fileContents = file.readlines()
file.close()
reverseContents = fileContents.reverse()
reversedFile = open(reverseContents, "wt")
for item in fileContents:
reversedFile.write(item)
reversedFile.close()
print fileContents
How does this look?
def reverseFile(filename):
file = open(filename,"rt")
fileContents = file.readlines()
file.close()
fileContents.reverse()
print fileContents
reversedFile = open(filename,"wt")
for item in fileContents:
reversedFile.write(item)
reversedFile.close()
reversedFile = open(filename,"rt")
fileContents = reversedFile.read()
reversedFile.close()
print fileContents
I just copied and pasted it from the CoWeb. Dina
emre soytürk
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