On 2020-03-08 10:05, Shrinivas Kulkarni wrote:
Hello Everyone
While writing python code, I frequently come across the need to do
certain tasks based on combined conditions.
Much of the task for all the sub-conditions are common but some are
specific to one or more of these sub-conditions.
A simplified example:
########################## Code ##########################
if (color == BLUE and count == 20) or (color == RED and count % 5 == 0):
rotate_the_wheel() # Common to the two sub-conditions
if(color == BLUE and count == 20): # First sub-condition
set_signal()
if(color == RED and count % 5 == 0): # Second sub-condition
clear_signal()
proc_post_rotate() # Common to the two sub-conditions
I am not sure if there is a better way to do this. If not, maybe there
can be an extension to the language, which would allow marking a
sub-condition just like we mark a sub-expression in a regular
expression.
Tentative syntax for this could be ({} marks the sub-condition and
\number refers back to it):
########################## Code ##########################
if {(color == BLUE and count == 20)} or {(color == RED and count % 5 == 0)}:
rotate_the_wheel()
if(\1): # First marked condition
set_signal()
if(\2): # Second marked condition
unset_signal()
proc_post_rotate()
An expression { ... } is already defined as a set.
And like sub-expressions, the nesting of marked sub-condions should
also be possible:
########################## Code ##########################
if {{(color == BLUE and count == 20)} and {value == 20}} or {(color ==
RED and count % 5 == 0)}:
if(\1):# Refers to the entire subcondition {{(color == BLUE and
count == 20)} and {value = 20}}
proc1()
if(\2):# Refers to sub-subcondition {value == 20}
This will not only avoid the repetition of sub-conditions, but make
code readable since something like \1 will give an immediate
indication of a sub-condition that's defined earlier.
Please let me know something similar is already implemented.
Even otherwise, all your thoughts, inputs and criticism are welcome.
In Python 3.8+ there's the "walrus operator" which lets you assign
within an expression:
if (first := (color == BLUE and count == 20)) or (second := (color ==
RED and count % 5 == 0)):
rotate_the_wheel()
if first:
set_signal()
if second:
unset_signal()
proc_post_rotate()
However, this has the problem that if the first subexpression is true,
the second will not be evaluated, so 'second' would not be set.
The simplest and clearest solution is just to write:
first = color == BLUE and count == 20
second = color == RED and count % 5 == 0
if first or second:
rotate_the_wheel()
if first:
set_signal()
if second:
unset_signal()
proc_post_rotate()
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