Non-local references, Python Programming

Non-local references

So far, whenever we needed to compute a variable, there  was  a binding for that  variable in the 'local' environment (the environment in which  we were evaluating the expression). But take this code:

 

def biz(a):

return a + b

 

>>> b = 6

 

2176_Non-local references.png

 

We need to elaborate, slightly,  how it is that a variable v is computed in an environment E:

 

  • We take if there is a binding for v in E; if so, we stop and return it.

 

  • If not, we compute v in the parent environment of E. If E has no base, we create an error.

 

It is important to check that this method  will continue up an arbitrarily long chain of environ­ ments  and their parents until either a binding for v is found or there are no more environments to examine.

So, in our case, we will compute the expression a + b in environment E2. We start by calculating a and searching value 2 in E2. Then, we compute b and cannot search it in E2...but we don't panic! We take the parent pointer to E1 and  try again.  We search a binding for b in E1 and  get the value  6. So, the value  of a + b in E2 is 8.

 

Posted Date: 8/11/2012 2:43:21 AM | Location : United States







Related Discussions:- Non-local references, Assignment Help, Ask Question on Non-local references, Get Answer, Expert's Help, Non-local references Discussions

Write discussion on Non-local references
Your posts are moderated
Related Questions
#question.Program 10 Assignment (Banking Objects – Savings/Checking Accounts) Create a program named 10.py that performs the following: Create a class named ChkAcct, and a class n

We encourage you to adopt an interactive style of debugging and programming. Use the Python shell a lot. Write short pieces of code and check them.  It is much  simpler to test the


Every programming language has to have  some method for indicating grouping of operations. Here is how you execute an if-then-else structure in Java:   if (s == 1){ s = s

how do you make an if and else statment work in pytho?

Write an algorithm for the sum of the given series 1,-1/2,1/4,-1/8.....

Python  Style Software  engineering courses  often  provide very  rigid  guidelines on the style of programming, generally the appropriate value of indentation, or what  to us

There are three seating categories at a stadium. For a softball game, Class A seats cost $15, Class B seats cost $12, and Class C seats cost $9. Write a program that asks how many

how to use re.sub to seperate distint words and phrases when translating text from English to Spanish or vis versa in python programming

Write a program that asks the user to enter a number of seconds. The responses of the program will vary depending on the length of seconds: • If the number of seconds is under 60