/study_chenPython

Primary LanguagePython

Python

Data

data type

Boolean, Int, Long, Float

Data Structure

Basic DS:

Import collections:

  • deque, Counter, OrderedDict, defaultdict, namedtuple

  • reference

Higher level:

  • heapq, Queue

Need Implement:

  • Trie

Article:

[1] basic

[2] basic & import

[3] heapq

Implement

####Heap

####Trie

Coding

Pythonic

#empty string can use not a
a = ""
if not a:
	#run /w empty a
#Created object can have dynamic attributes, built-in DS cannot
class Object(object):
	pass
aa = Object
aa.flag = True #add flag dynamically
if hasattr(aa,'flag'):
	print aa.flag #print True

bb = {}
try:
	bb.flag = True
except Exception, e:
	print e #'dict' object has no attribute 'flag'


Higher Performance


String Related


# use join instead of +=
a = ["as", "you", "sunny"]
res = " ".join(a)

#print
a = {'a': 1, 'b':2}
res = "hello %(a)s and %(b)s" %a


Loop Related


# map > local & dot > basic
# map(func, iter) call func for every iter, not good for overlap operation
# record .func as lcoal variable
# use xrange() instead of range()
oldlist = "asdfs"
newlist = []
newlist = map(str.upper, oldlist)

upper = str.upper
append = newlist.append()
for var in oldlist:
    append(upper(var))


Dictionary


# try is better than if
# use .get(index, 0)
# use collections.defaultdict


Calculate


# + > >> or << > * or /


Profiling


# several module


Memory access


Touch address


# id()

# iterator
a = [1,2,3,4]
b = iter(a)
print next(b)


Tricks


    

  • 

    x = a or b
    

    #one of a,b is equal to None
if a or b:
    x = a or b
    

    • 

  • 

    hasattr() check whether it has additional attributes
    

    while newHead != None:
    if hasattr(newHead,'flag') and newHead.flag == True:
        return newHead
        newHead.flag = True
    return None
    

    • 

  • 

    print
    

      

    • 

      without newline
      

      #the last , is indicate
print str(node.value) , "->" ,
      

      • 

    • 

      any format
      

      a = [1,2,3]
print "the list:%r" %a
      

      • 

    

    • 



Structure & Design Skill


    

  • 

    OOP
    

      

    • 

      class variable & object variable
      

      • 

    • 

      no virtual function like C++
      

      • 

    • 

      don't touch member directly
      

      • 

    

    • 

  • 

    Structure
    

      

    • 

      multi-file use os and sys module to change path
      

      • 

    • 

      module
      

        

      • __name__: __main__ or module
        • 

      

      • 

    

    • 



Fault List


    

  • 

    and instead of &&
    

    • 

  • 

    create intersection link list
    

    

    cannot append multiple nodes one by one to 2 link lists, because when we append them to the 1st list, all nodes are linked together, for the 2nd list, there will be circle.
    

    

    • 

  • 

    file name cannot be string.py
    

    • 



Reference


[1] Pythonic


[2] Improve Performance


[3] Except System