[python-win32] A Suggestion for Python Syntax
Hung, Le Khanh
softex@hn.vnn.vn
Sun, 3 Nov 2002 10:36:16 +0700
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We all know that the statement like continue, break, .. are not =
structured.
But they are useful for flexible control of the execution. It is mainly
because of loop structure limitations.
Here we suggest a strengthened loop and selective constructions. With =
them
we need not to use break statement at all.
CompoudStatement ::=3D dostatement | loop statement
dostatement::=3D
"do" suite
GuardedCommand
loopstatement::=3D
"loop" suite
GuardedCommand
GuardedCommand::=3D
( ?[!] "check" Condition suite )*
Condition ::=3D expression :
Condition ::=3D
( "case" Condition suite )*
These constructions could replace all Python's compound statements
Some examples:
1. Python command
if B1 : S1
elif B2 : S2
else S3
is equivalent to
do
?! check case B1 : S1
case B2 : S2
S3
2. Python command
while B : S
is equivalent to
loop
? check B : S
3. # Search in Array
# This is common sketch for searching algorithms
InitSearchScope
loop
? check NotEmptySearchScope:
TakeAnElement
? check NotFit:
SrinkSearchScope
# Implementation of Sequential Search
i =3D lo; # Scope is from lo to hi
loop
? check i < hi : # i is in Scope
? check a[i] !=3D x :
i+=3D1
# Binary Search
i,j =3D lo,hi
loop
? check i<j : k =3D (i+j) / 2
? check
case a[k]<x : i =3D k+1
case a[k]>x : j =3D k-1
This bit of code has the same structure as the previous!
# For comparison, here is Python's Binary search
i,j =3D lo,hi
while i<j : k =3D (i+j) / 2
if a[k]<x : i =3D k+1
elif a[k]>x : j =3D k-1
else break
It is not obvious and natural here that there are two exit points from =
the loop.
I would be happy to receive comments
Best regards.
Hung
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<DIV><FONT face=3DArial size=3D2>We all know that the statement like =
continue,=20
break, .. are not structured.<BR>But they are useful for flexible =
control of the=20
execution. It is mainly<BR>because of loop structure =
limitations.<BR>Here we=20
suggest a strengthened loop and selective constructions. With them<BR>we =
need=20
not to use break statement at all.<BR><BR><BR>CompoudStatement ::=3D =
dostatement |=20
loop statement<BR>dostatement::=3D<BR> "do"=20
suite<BR> =20
GuardedCommand<BR>loopstatement::=3D<BR> "loop"=20
suite<BR> =20
GuardedCommand<BR>GuardedCommand::=3D<BR><BR> ( ?[!] =
"check"=20
Condition suite )*<BR>Condition ::=3D expression :<BR>Condition=20
::=3D<BR> ( "case" Condition suite )*<BR>These=20
constructions could replace all Python's compound =
statements<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>Some examples:<BR>1. Python=20
command<BR><STRONG>if</STRONG> B1 : S1<BR><STRONG>elif</STRONG> B2 :=20
S2<BR><STRONG>else</STRONG> S3<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>is equivalent =
to<BR><BR><STRONG>do</STRONG><BR>?!=20
<STRONG>check</STRONG> <STRONG>case</STRONG> B1 :=20
S1<BR> &=
nbsp; =20
<STRONG>case</STRONG> B2 : =
S2<BR> =20
S3<BR>2. Python command<BR><STRONG>while</STRONG> B : S<BR>is equivalent =
to<BR><STRONG>loop</STRONG><BR>? <STRONG>check</STRONG> B : =
S<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>3. # Search in Array<BR># This is =
common sketch for=20
searching algorithms<BR>InitSearchScope<BR><STRONG>loop</STRONG><BR>?=20
<STRONG>check</STRONG>=20
NotEmptySearchScope:<BR> =20
TakeAnElement<BR>? <STRONG>check</STRONG>=20
NotFit:<BR> =20
SrinkSearchScope<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2># Implementation of Sequential =
Search<BR>i =3D=20
lo; # Scope is from lo to hi<BR><STRONG>loop</STRONG><BR>?=20
<STRONG>check</STRONG> i < hi : # i is in Scope<BR>? =
<STRONG>check</STRONG>=20
a[i] !=3D x :<BR> =
i+=3D1<BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2># Binary Search<BR>i,j =3D=20
lo,hi<BR><STRONG>loop</STRONG><BR>? <STRONG>check</STRONG> i<j : k =
=3D (i+j) /=20
2<BR>? =
<STRONG>check</STRONG><BR> =20
<STRONG>case</STRONG> a[k]<x : i =3D=20
k+1<BR> <STRONG>case</STRONG>=20
a[k]>x : j =3D k-1<BR><BR>This bit of code has the same structure as =
the=20
previous!<BR><BR># For comparison, here is Python's Binary search<BR>i,j =
=3D=20
lo,hi<BR><STRONG>while</STRONG> i<j : k =3D (i+j) /=20
2<BR> <STRONG>if</STRONG> =
a[k]<x :=20
i =3D k+1<BR> =
<STRONG>elif</STRONG>=20
a[k]>x : j =3D k-1<BR> =20
<STRONG>else</STRONG> <STRONG>break</STRONG><BR></FONT></DIV>
<DIV><FONT face=3DArial size=3D2>It is not <EM>obvious</EM> and =
<EM>natural</EM>=20
here that there are two exit points from the loop.<BR>I would be happy =
to=20
receive comments<BR>Best regards.<BR>Hung<BR></DIV></FONT></BODY></HTML>
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