[Tutor] Mysterious syntax errors and file-reading issues

[Alan Gauld]

> def exists('/Users/username/Documents/python/word_bank.txt'):
>    return os.access('/Users/usernameDocuments/python/word_bank.txt',

> 1.  I get a "syntax error" message at the line that starts with "def
> exists", but I don't see the mistake.


You are defining a function with a constant as an agument.
You cannot do that you need a variable (technically a parameter)
The parameter can have a default value if you like so:

> def 
> exists(filename='/Users/username/Documents/python/word_bank.txt'):
>    return os.access(filename,



> os.F_OK)
> for line in
> open('/Users/username/Documents/python/word_bank.txt').readlines():

> 2.  If I take out that line, I get "errno 2" at the next line; the
> interpreter seems convinced that that file doesn't exist, though it 
> does.

defining a function is different from executing it. After the 
definition
you still need to call it and check the result.

However usually its good enough just to use a try/except to catch
errors for missing files. In pseudo code like this:

try:
    for line in open(filename):
       process line
except: print ooops couldn't process file!

You only need to use exists() if you really need the detail of why
it failed - maybe with a view to taking corrective action before 
trying
again...

Alan Gauld
Author of the Learn to Program web site
http://www.freenetpages.co.uk/hp/alan.gauld