Procedure calls, Python Programming

Procedure calls

When you compute an expression of the form

(,  ..., )

 

the Python interpreter treats  this as a procedure call. It will be simpler to talk about  a speci?c case of invoking a function, so we will explain with the example

 

>>> square(a + 3)

 

computed in environment E1. Here are the steps:

 

1.  The expression that determines the procedure () is computed. In this case, we compute

square in E1 and get Procedure1.

 

2.  The expressions that  determine the arguments (, ..., )  are computed. In this case, we compute a + 3 in E1 and get 5.

 

3.  A new environment (in this case E2) is prepared, which:

-  binds  the formal  parameters of the function (in this case x) to the values  of its arguments(in this case, 5); and

-  has as its base the environment in which  the procedure was de?ned we ?nd  a pointer .

 

1843_Procedure calls.png

 

The dotted line between E1 and  E2 is used to show that  E1 is the parent environmentof E2.

 

4.  The statements of the  procedure body  are computed in the  new  environment until  either  a return statement or the end of the list of statements is got. If a result expression is calculated, the expression after the return is computed and its value is returned as the value of the function call expression. Otherwise, the function has no return value,  and  the expression has the unique Python value  None.

 

In our  example, the  only  statement in the  body  is a return statement.  So, we  compute the expression x * x in E2, obtaining a value  of 25.  That  value  is returned as the value  of the entire  procedure-call expression square(a + 3).

 

This basic mechanism can generate behavior of arbitrary hardness, when grouped with  recursion or other control  structures.

 

 

 

 

Posted Date: 8/11/2012 2:04:23 AM | Location : United States







Related Discussions:- Procedure calls, Assignment Help, Ask Question on Procedure calls, Get Answer, Expert's Help, Procedure calls Discussions

Write discussion on Procedure calls
Your posts are moderated
Related Questions
1)    Write a python programmecomparing for and while loops like the following. Math Times table For Loop: 2x1=2 2x2=4 ..... 2x12=24 While Loop: 3x1=3 3x

Displaying random geometric graphs in an uniform square, unit disk, dense rim unit disk, and uniform sphere

Procedures as First-class objects In Python, unlike  many  other  languages, methods are behave in much  the same way as num­ bers:  they  can be stored as values  of variable

I need server, client and trusted side communicating and charging a service with that protocol (or needham shroeder)

Python programs Every  general-purpose computer has a various detailed design, which  defines  that  the way  its program requires  to be specified is different. The "machine

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

Print vs Return Here are two different method declarations: def f1(x): print x + 1 def f2(x): return x + 1 What happens when  we call them? >>> f1(3) 4 >>

Primitives, Composition, Abstraction, and Patterns   We will  start  by thinking about  how  the  PCAP  framework applies to computer programs, in general. We may do that by

from urllib2 import urlopen var= ('' response">http://placekitten.com'') response = kittens.read(body) body = response[559:1000] print ''Kittens:'', response

Data array A has data series from 1,000,000 to 1 with step size 1, which is in perfect decreasing order. Data array B has data series from 1 to 1,000,000, which is in random order.