Python：使用2元组列表定义函数的最快方法

Question

Suppose L is a list of two tuples, with len(L)~16,000 .

An element of L is of the form (x,y) where in my case x is itself a list of 7 elements and y is a float.

How can I define a function f such that it computes f(x)=y using L ? Right now I am using the naive code:

def f(x):  
    for i in range(0,len(L)):
        if x==L[i][0]:
           return L[i][1] 

But this is taking way too long. Any suggestions to make this run faster?

Answer 1

tabulate = dict(L)
f = tabulate.get

This will work as long as you use tuples for your keys instead of lists.

Answer 2

What you're implementing is called an association list, for example:

L = [ ('x', 1), ('y', 2), ('z', 3) ]

A far better data structure to use in Python would be a dictionary:

D = { 'x':1, 'y':2, 'z':3 }

Look, you can even transform an association list into a dictionary:

D = dict(L)

Now you can quickly retrieve any value from it:

D['y']
=> 2

Answer 3

Try using a dict, a list of key-value pairs that you can use to do lookups, it would be perfect for your "function"

Here is an overview of the python dict datatype:

http://www.tutorialspoint.com/python/python_dictionary.htm