Python Performance Optimization Tips

1 Dictionaries and lists

The Python dictionary uses a hash table, so the complexity of the lookup operation is O (1), and the list is actually the array, in the list, the lookup needs to traverse the entire list, its complexity is O (n), so the operator dictionary of lookup access to members is faster than list.

From time Import time

T = time ()

list = [' A ', ' B ', ' is ', ' python ', ' Jason ', ' Hello ', ' hill ', ' with ', ' phone ', ' test ',

' Dfdf ', ' apple ', ' PDDF ', ' ind ', ' basic ', ' none ', ' baecr ', ' var ', ' Bana ', ' dd ', ' WRD ']

#list = Dict.fromkeys (list,true)

Print List

Filter = []

For I in Range (1000000):

For find in [' was ', ' hat ', ' new ', ' list ', ' old ', '. ']:

If find not in list:

Filter.append (Find)

Print "Total run time:"

Print time ()-T

The above code will probably need 16.09seconds to run. If the line #list = Dict.fromkeys (list,true) Comment is removed, the list is converted to a dictionary and then run, and the time is approximately 8.375 seconds, which is about half the efficiency increase. Therefore, using dict instead of list is a good choice when multiple data members are needed for frequent lookups or visits.

2 Sets and lists (list)

The union,intersection,difference operation of set is faster than the iteration of the list, so if a list intersection is involved, the set, or the bad problem can be converted to set to operate

Finding the intersection of lists

From time Import time

T = time ()

LISTA=[1,2,3,4,5,6,7,8,9,13,34,53,42,44]

LISTB=[2,4,6,9,23]

Intersection=[]

For I in Range (1000000):

For a in Lista:

For B in Listb:

If a = = B:

Intersection.append (a)

Print "Total run time:"

Print time ()-T

The operating time of the above program is roughly:

Total run Time:

38.4070000648

Optimized code Listing:

From time Import time

T = time ()

LISTA=[1,2,3,4,5,6,7,8,9,13,34,53,42,44]

LISTB=[2,4,6,9,23]

Intersection=[]

For I in Range (1000000):

List (set (Lista) &set (LISTB))

Print "Total run time:"

Print time ()-T

The running time of the program is reduced to 8.75, and the running time is greatly shortened after the set is changed to 4 times times.

Table 1. Common usage of Set

syntax	action
	union
	intersection
Set (List1) –set (LIST2)	Difference	The collection of elements appearing in List1 but not appearing in List2

Python Performance Optimization Tips