Python：函数调用后的类属性消失

Question

so such a problem, that i can't figure it out. Maybe i have too little Python knowledge.

The problem is, that after this function runs once smoothly, another time i get error in another function.

Function, after which things break:

    def setFixedPriority( self, priority, lister ):
    step = priority / lister . __len__ ( )
    for j in range( 0, lister . __len__( ) ):
        for i in range( 0, self . listOfJobs . __len__ ( ) ) :
            if self . listOfJobs[ i ] . category == lister[ j ]:
                self . listOfJobs[ i ] . priority += priority
            elif self . listOfJobs[ i ] . jobType == lister[ j ]:
                self . listOfJobs[ i ] . priority += priority
            elif self . listOfJobs[ i ] . timeToDo == lister[ j ]:
                self . listOfJobs[ i ] . priority += priority
        priority -= step
            self . sortByPriority( )

Function in which appears the problem:

    def sortByPriority( self ) :
    tmp = range ( 1, self . listOfJobs . __len__ ( ) + 1 )
    for i in reversed ( tmp ) :
        for j in range ( 1, i ) :
            if self . listOfJobs [ j - 1 ] . priority < self . listOfJobs [ j ] . priority :
                self . listOfJobs [ j - 1 ], 
                self . listOfJobs [ j ] = self . listOfJobst [ j ], 
                self . listOfJobs [ j - 1 ]

Calling the function (From different python script/file/class):

    self . jobs . setFixedPriority( int( self . settings[ 'Spinbox1' ] ), self . settings[ 'type' ] . split( ":" ) )

And the error i get:

    File "data/ToDoListClass.py", line 82, in sortByPriority
    self . listOfJobs [ j ] = self . listOfJobst [ j ], 
    AttributeError: jobList instance has no attribute 'listOfJobst'

I know that the sortByPriority works OK, because i am calling this once before setFixedPriority and it does not give me errors.

What could cause this to happen?

Answer 1

AttributeError: jobList instance has no attribute 'listOfJobst'

If you look closely, you have a typo there. The attribute is called listOfJobs without a trailing t .

Note that while this will make go of the error, this will probably not fix the function:

self . listOfJobs [ j - 1 ], 
self . listOfJobs [ j ] = self . listOfJobs [ j ], 
self . listOfJobs [ j - 1 ]

That construct is probably supposed to swap listOfJobs[j] and listOfJobs[j - 1] . Due to the line breaks, this will do the following though:

1. Make a one-tuple with listOfJobs[j - 1] (nothing else happens with that)
2. Assign a one-tuple with listOfJobs[j] to listOfJobs[j] .
3. Access listOfJobs[j - 1] (again, nothing else happens).

What you want to do is to write it either in one line:

self.listOfJobs[j - 1], self.listOfJobs[j] = self.listOfJobs[j], self.listOfJobs[j - 1]

Or if you want to keep line breaks, use Python's \\ syntax to make the line continue:

self.listOfJobs[j - 1], \
self.listOfJobs[j] = self.listOfJobs[j], \
self.listOfJobs[j - 1]

Although I would argue if that makes it really clear what happens.

Finally, you can clean your code up a lot. You can directly iterate over lists, and you can also check multiple conditions in a single if. And lastly, Python's sort function allows you to specify a custom comparison function so that you don't need to implement an own sorting algorithm but can use Python's implementation. All in all, you could for example end up with just something like this:

def setFixedPriority (self, priority, listers):
    step = priority / len(listers)
    for lister in listers:
        for job in self.listOfJobs:
            if job.category == lister or job.jobType == lister or job.timeToDo == lister:
                job.priority += priority

        priority -= step

    self.listOfJobs.sort(key=lambda x: x.priority)

Answer 2

A few notes that will help you write more "Pythonic" code:

• Your code isn't very Pythonic. You don't need to use range() here; you can use for ... in constructs that are fewer lines and more clear. But that's not your main problem.
• sortByPriority() should rewritten to use the built-in Python sort function; you can give it an arbitrary function by which to sort the two comparators. That's really what you want to do here rather than rewrite sort() .

One thing you're doing that's bitten me a few times is that you're sorting a list while in the middle of iterating on it. This has caused bizarre behavior for me in the past, including breakage. This might work OK for your uses, but you should consider not sorting it until you're done tweaking everything you want in the list.

Lastly, I don't see where you create listofjobst . Is that a typo?