Simple expressions, Python Programming

Simple expressions

A cornerstone of a programming language is the  ability  to compute expressions.  We will start here  with  arithmetic expressions, just to take the  concept.   An expression consists  of a sequence of 'tokens' that show the application of operators to data component. Each expression has a number,  which  may be computed recursively by evaluating primitive expressions, and then using  standard principles to combine their values  to get new variables. Numerals, such -3.7 as or 6  are expressions, whose  numbers  are  numeric constants. Their numeric values  can be integers, within some  range  dictated by the  programming language, or ?oating point  variables. Floating  point  variables are used  to represent non-integer values,  but they  are not related, in many  important types,  from  the  real  numbers.  There  are in?nitely many real numbers within a ?nite  difference, but  only  finite various  ?oating-point numbers exist at all.  In fact, the normal laws of real arithmetic (transitivity, associativity, etc.)  are created in ?oating-point arithmetic, because  the results of any provided sub-computation may not be representable in the given number of bits.

 

We will explain the calculation of expressions in Python by showing short  transcripts of interactive sessions  with the Python shell : the shell is a computer program that

  • Prompts the user for a relation, by typing »>,
  • Reads what the user types in, and changes it into a set of tokens,
  • Parses the tokens into a data structure showing the syntax of the expression,
  • Computes the parsed expression using an interpreter, and
  • Prints out the resulting value

 

So, for example, we might  have this interaction with Python:

>>> 2 + 3

5

>>> (3 * 8) - 2

22

>>> ((3 * 8) - 2) / 11

2

>>> 2.0

2.0

>>> 0.1

0.10000000000000001

>>> 1.0 / 3.0

0.33333333333333331

>>> 1 / 3

0

There are a couple  of things  to look here.  First, we can look how  ?oating point  values only approximately represent real numbers: when  we write in 0.1, the closest Python can take it in ?oating point  is 0.100000000000001.  The end interaction is particularly troubling: it seems like the value of the expression 1 / 3 should be something like 0.3333.  However, in Python, if both registers to the / operator are integer number, then it will operate an integer division.

 

These expressions can be arbitrarily deeply nested combinations of primitives. The laws used  for calculation are essentially the same as the ones you learned in school; the interpreter proceeds by applying the operations in precedence order13,  calculating sub-expressions to get new variables,  and then calculating the expressions those values  takes in, until in one value  results.

 

Posted Date: 8/11/2012 1:32:28 AM | Location : United States







Related Discussions:- Simple expressions, Assignment Help, Ask Question on Simple expressions, Get Answer, Expert's Help, Simple expressions Discussions

Write discussion on Simple expressions
Your posts are moderated
Related Questions
Write a program that requests a password after the author/program information is displayed. Make the password "hello". The program should then ask the user for their name: if the n

program on damped lcr cicuit

In Python, the fundamental abstraction of a computation is as a procedure (other  books call them "functions" instead; we will end  up  using  both  values).   A function that  tak

Write a Python program to accomplish the following. Use modular design. Include at least 3 functions: one that returns zero values, one that returns one value, and one that retu

List Comprehensions   Python has a very nice built-in  facility for doing  many  iterative methods, known as list comprehensions. The basic template is       [

Your task is to construct a translator from the subset of Python in Project 3 intocontinuation-passing style (CPS). Of course, the expected way of accomplishing this is to trans

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

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

The goal of this exercise is to write a \business phrase" generator, which each time it is called produces lines of business speak, such as: It's time that we became uber-effici

Non-local references in procedures There  is an important subtlety in the  way  names  are handled in the  environment created by a function call. When  a value  that  is not