[pythonvis] Re: Yet another indenting explanation
- From: Joseph Lee <joseph.lee22590@xxxxxxxxx>
- To: pythonvis@xxxxxxxxxxxxx
- Date: Wed, 14 May 2014 22:03:45 -0700
Hi,
For classes and functions, you'd enclose the content/subroutine
one level below the class/function declaration.
Cheers,
Joseph
----- Original Message -----
From: "Jaffar.sidek10@xxxxxxxxx" <jaffar.sidek10@xxxxxxxxx
To: <pythonvis@xxxxxxxxxxxxx
Date sent: Thu, 15 May 2014 13:01:21 +0800
Subject: [pythonvis] Re: Yet another indenting explanation
Hi Richard. Thanks for this. Just a point of clarification.
following the same satement as in your email, ;do the second and
third lines of the statement occupy the same indent level?
what about if the statement incapsulates a class like this:
class window:
dif __Init__(self, ...):
display.window()
then what should be the levels of indent?
Cheers and thanks.
From: Richard Dinger
Sent: Thursday, May 15, 2014 12:21 PM
To: pythonvis@xxxxxxxxxxxxx
Subject: [pythonvis] Yet another indenting explanation
Many years ago the computer scientist Edsger Dijkstra
demonstrated that any program can be structured out of
combinations of the following four basic constructs:
1 A sequence of statements: execution of the statements is
sequential.
2 Branch or conditional control-statement: execution branches to
a different subordinate statement sequence depending on some
condition.
3 loop control-statement: execution of a subordinate sequence of
statements is repeated until some condition is met.
4 function call statement: execution jumps to a subordinate
statement sequence and then continues immediately after the point
of the function call.
So how is a subordinate statement sequence specified in the
source code? Different programming languages use different
approaches. Note the term statement block may also be used.
Algol languages use begin and end to delimit the sequence as in
the following if-statement:
if x < 0 then
begin
x = abs(x)
count = count + 1
end
The C family of languages use braces for a more mathematical
looking approach. In C languages the same if-statement is:
if (x < 0)
{
x = abs(x)
count += 1
}
And Python simply uses the indenting alone like this:
if x < 0:
s = abs(x)
count += 1
You must tell the computer somehow what statements are to be
executed when a control-statement is executed. Python uses the
indentation and nothing else. So in our example, the two
statements are indented one more level from the level of the
controlling if statement's level and the subordinate statement
sequence continues until the indenting returns to a lower level.
Note that this is laid out like an outline or a set of help
files where each subsequent level is indented one more level to
the right.
The rules for indenting are simple. Start at the left margin in
a file or level0. Control-statements introduce subordinate
statement sequences of one or more statements, which are indented
to the next level. You cannot increase indentation except after
a control statement such as a loop or conditional. Note all such
statements end in a colon. The block of indented statements ends
when the level of indentation decreases to a previous level.
If you are still uncertain, try writing some short nonsense
programs where you can test indenting. Try a sequence of two
print statements and then a third print one level deeper. What
happens?
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