1. THE PYTHON STD LIB BY
EXAMPLE – DATA
STRUCTURES
John
Saturday, December 21, 2013

2. Overview of this class
• Python already include several standard
programming data structures, such as
list,tuple,dict and set.
• The collection module include other several
data structures, such as Deque, defaultdict,
OrderDict and namedtuple.
• For large amount of data, an array module is
more efficient

3. THE COLLECTION
MODULE

4. Data type Counter
• A container tracks how many times
equivalent values are added.

5. Update() method of Counter
• The count value will be increased based on
the new data, rather than replaced.

6. More functions in Counter class
• c[i]: return the count of i.
• c.elements(): return an iterator
• c.most_common(3): produce a list in order of
frequency
• c.update({‘a’:1,’b’:5}): The count value will be
increased based on the new data, rather than
replaced.

7. Data type defaultdict
Similar as dict.It can let the caller specify the
default value when container is initialized.

8. Data type deque
• Support adding and removing elements from
either end.

9. More method in deque
•
•
•
•
Method extend,extendleft
Method append,appendleft
Method pop,popleft
Method rotate: rotate the deque to the right
direction

10. Data type namedtuple
• Similar as regular tuple, but can use
instance.attr to access the elements

11. Data type OrderDict
• A dictionary subclass that remember the
order.

12. Data type heapq
• A min-heap: a tree like data structure that
the parent should be less than or equal to its
children.
• Binary heap use a list or array represent it.
The children of element
N is 2*N+1 and 2*N+2(
zero based indexes).

13. Function of heapq class
Heap =[]
•method: heapq.heappush(Heap,n): add n into
heap.
•Method: heapq.heapify(list): sort list as a heap
•Method heapq.heappop(Heap): pop the smallest
item
•Method heapq.heapreplace(heap,n): replace the
smallest item with n.

14. Data type bitsect
• Purpose is maintain a list in sorted order
without having to call sort each time adding
new item.

15. Method of bitsect
• Method insort(alias of insort_right): insert
after the existing value
• Method insort_left: insert before the existing
value.
• Method bisect(alias bisect_right): return the
position after the existing value.
• Method bisect_left: return the position
before the existing value.

16. Data type Queue
• The Queue module provides FIFO (first in,
first out) data structure suitable for
multithreaded programming.

17. Data type LIFO Queue (Stack)
• LifoQueue use LIFO (Last in, first out)
(normally we call it stack data structure).

18. Data type PriorityQueue
• The process order is based on characteristics
of those items, rather than the order.
Example code see here:
Import Queue
q = Queue.PriorityQueue()

19. THE WEAKREF
MODULE

20. Brief introduction
• The weakref module support weak
references to objects.
• A normal reference increase the reference
count on the object and prevent it from
being garbage collected.

21. Example of weakref
• Class ref to create a weak reference
• Ref will return None
if obj is deleted.

22. THE COPY MODULE

23. Brief introduction
• Provide functions for duplicating objects
using shallow or deep copy semantics
• The copy module include two functions,
copy() and deepcopy().

24. Shallow copy: copy()
• A new container populated with references
to the contents of the original object.

25. Deep copies: deepcopy()
• A New container populated with copies of
the contents of the original object.
• It is possible to control hwo copies are made
using the __copy__() and __deepcopy__()
special methods.

26. THE PPRINT
MODULE

27. Quick example of pprint
• The pprint module contains a “pretty
printer”

28. Work with custom classes
• If class define __repr__() method, pprint()
can also work.

29. More options
• Option depth: control the print depth for
very deep data strctures.
>>> pprint(data,depth=1)
• Option width: default output width is 80
columns.
>>> pprint(data, width=5)

30. Reference
• Source code
https://bitbucket.org/qzhang03022/py_stdlib_by