|
Original |
Translation |
|
97
|
Using the current reference counting and destructor scheme, each new assignment to f closes the previous file. Using GC, this is not guaranteed. If you want to write code that will work with any Python implementation, you should explicitly close the file or use the :keyword:`with` statement; this will work regardless of GC::
|
|
|
98
|
for file in very_long_list_of_files: with open(file) as f: c = f.read(1)
|
|
|
99
|
Why isn't all memory freed when Python exits?
|
|
|
100
|
Objects referenced from the global namespaces of Python modules are not always deallocated when Python exits. This may happen if there are circular references. There are also certain bits of memory that are allocated by the C library that are impossible to free (e.g. a tool like Purify will complain about these). Python is, however, aggressive about cleaning up memory on exit and does try to destroy every single object.
|
|
|
101
|
|
102
|
Why are there separate tuple and list data types?
|
|
|
103
|
Lists and tuples, while similar in many respects, are generally used in fundamentally different ways. Tuples can be thought of as being similar to Pascal records or C structs; they're small collections of related data which may be of different types which are operated on as a group. For example, a Cartesian coordinate is appropriately represented as a tuple of two or three numbers.
|
|
|
104
|
Lists, on the other hand, are more like arrays in other languages. They tend to hold a varying number of objects all of which have the same type and which are operated on one-by-one. For example, ``os.listdir('.')`` returns a list of strings representing the files in the current directory. Functions which operate on this output would generally not break if you added another file or two to the directory.
|
|
|
105
|
Tuples are immutable, meaning that once a tuple has been created, you can't replace any of its elements with a new value. Lists are mutable, meaning that you can always change a list's elements. Only immutable elements can be used as dictionary keys, and hence only tuples and not lists can be used as keys.
|
|
|
106
|
How are lists implemented?
|
|