program for comparisons in python

I'm reall开发者_如何学Cy new to programming (really, really new) and need help with the basics. I'm trying to write a program with python that will compare the contents of two .txt files, one a reference and the other the source. The contents are a simple random listing of names, and I want it to print out if there are any names in the source that are not in the reference.

I've looked at other stuff on this site but every time I tried it, the terminal would never actually give a result, even if there was a print command in the program.

I also have a hard time reading the language of a program and ascertaining it's exact function, so something with clear directions would be really appreciated.

As far as I have is:

ref = open("reference.txt")
sor = open("source.txt")

list1 = ref.read()
list2 = sor.read()

for i in list2:
    if i != list:
    print i

ref.close()
sor.close()

And when I try and run this, it says "expected an indented block"? at the 'print i' line. Why?

Please help me out, as I have to teach myself this stuff and am not doing too well.

Thanks.

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If you are totally, completely new to programming then it will take you some time to be able to implement what you describe. Take a step back, pour yourself a beverage, and start here. Start at the beginning, and repeat each illustration until you understand.

http://docs.python.org/tutorial/

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As previously mentioned, your inner if statement needs to be indented, as

for i in list2:
    if i != list:
        print i

This requires two indents because it is two nested blocks. As a basic rule of thumb, anywhere you're ending a line with a colon (:), you're starting a new code block, and should be indenting another level. This is so you can un-indent once to end the if block without ending the for block.

However, I doubt this will do what you want based on your description. It's likely you wanted something more like

sourceLines = set(sor.readLines())
for line in ref.readlines():
    if line not in sourcelines:
        print line

---

if blocks in python have to be indented, add another level of indent for your print i statement

for i in list2:
    if i != list:
        print i

---

These lines read the files as strings:

list1 = ref.read()
list2 = sor.read()

This loop iterates through the string one character at a time:

for i in list2:

This line compares the character to the list class:

    if i != list:

---

I'll answer your indentation error first: you need another 4 spaces before the print statement. In Python indentation is important and you need to indent any block and dedent to end that block.

For your problem I am going to not give you written out code in advance but more of a flow on how to do it:

1. Create 2 sets (http://docs.python.org/library/stdtypes.html#set-types-set-frozenset)
2. Read both files into a seperate set (you can do this while iterating over a file and appending to your set).
3. Compare your two sets using the set1 - set2 syntax (see the link above) to show all items not common to both sets.

Hope you can make it work from this.

Now for the code:

with open('file1.txt') as file1:
    set1 = set(line for line in file1)

with open('file2.txt') as file2:
    set2 = set(line for line in file2)

print set1 - set2

This uses some principles you are probably not familiar with (look up: list comprehensions, generator comprehensions and the previously noted link about sets which are unique collections).