[Tutor] Multiple for and if/else statements into a single list comprehension
Is it possible to get two nested for statements followed by a nested if/else statement all into a single list comprehension ie. the equivalent of the below: for i in xrange(1,20): for j in xrange(1,10): if j6: j=int(8+str(j)) else: j=int(9+str(j)) print %(i)02d_%(j)02d % locals() # double for statement without if/else works print \n.join([%(i)02d_%(j)02d % locals() for i in xrange(1,20) for j in xrange(1,10)]) #now try to incorporate if/else part #failed attempt 1 print \n.join([%(i)02d_%(j)02d % locals() for i in xrange(1,20) for j in xrange(1,10) j=int(8+str(j)) if j6 else int(9+str(j))]) #failed attempt 2 print \n.join([%(i)02d_%(j)02d % locals() for i in xrange(1,20) j=int(8+str(j)) if j6 else int(9+str(j)) for j in xrange(1,10)]) #failed attempt 3 print \n.join([%(i)02d_%(j)02d % locals() j=int(8+str(j)) if j6 else int(9+str(j)) for i in xrange(1,20) for j in xrange(1,10)]) Many thanks in advance. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Multiple for and if/else statements into a single list comprehension
Jignesh Sutar wrote: Is it possible to get two nested for statements followed by a nested if/else statement all into a single list comprehension ie. the equivalent of the below: for i in xrange(1,20): for j in xrange(1,10): if j6: j=int(8+str(j)) else: j=int(9+str(j)) print %(i)02d_%(j)02d % locals() Many thanks in advance. Need I say that it is a bad idea to build overly complex list comprehensions? Under that proviso: The first step is always to ensure that there is a single expression in the inner loop. I'm keeping as similar as possible to your loops: for i in xrange(1, 20): for j in xrange(1, 10): print %02d_%02d % (i, int((8 if j 6 else 9) + str(j))) Now the translation is mechanical for x in a: for y in b: expr becomes [expr for x in a for y in b] or (using a genexp rather than a listcomp as you are going to print it anyway) print \n.join( %02d_%02d % (i, int((8 if j 6 else 9) + str(j))) for i in xrange(1, 20) for j in xrange(1, 10)) But again: don't do that ;) By the way, using locals() is another bad idea, plus it does not capture the loop vars of genexps (all pythons) and listcomps (python3). PS: a simple alternative: print \n.join( %02d_%02d % (i, k) for i in range(1, 20) for k in range(81, 86) + range(96, 100)) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Multiple for and if/else statements into a single list comprehension
Peter Otten wrote: [locals()] does not capture the loop vars of genexps (all pythons) and listcomps (python3). Sorry, I was totally wrong on that one. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Multiple for and if/else statements into a single list comprehension
On 03/17/2014 11:22 AM, Jignesh Sutar wrote: Is it possible to get two nested for statements followed by a nested if/else statement all into a single list comprehension ie. the equivalent of the below: for i in xrange(1,20): for j in xrange(1,10): if j6: j=int(8+str(j)) else: j=int(9+str(j)) print %(i)02d_%(j)02d % locals() You can do it by reformulating your inner block into an expression (here, using a ternary if expression), which will then become the expression part of the comprehension. However, a few remarks: * don't do that: the only advantage is to make your code unreadable * you may reformulate using 2 comprehensions; if you don't want intermediate lists, use a generator expression for the inner one * above, the inner j is a new variable with a distinct meaning: why do you call it j? * do you really need string concat to perform arithmetic? d ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
[Tutor] Multiple for and if/else statements into a single list comprehension
Is it possible to get two nested for statements followed by a nested if/else statement all into a single list comprehension ie. the equivalent of the below: for i in xrange(1,20): for j in xrange(1,10): if j6: j=int(8+str(j)) else: j=int(9+str(j)) print %(i)02d_%(j)02d % locals() # double for statement without if/else works print \n.join([%(i)02d_%(j)02d % locals() for i in xrange(1,20) for j in xrange(1,10)]) #now try to incorporate if/else part #failed attempt 1 print \n.join([%(i)02d_%(j)02d % locals() for i in xrange(1,20) for j in xrange(1,10) j=int(8+str(j)) if j6 else int(9+str(j))]) #failed attempt 2 print \n.join([%(i)02d_%(j)02d % locals() for i in xrange(1,20) j=int(8+str(j)) if j6 else int(9+str(j)) for j in xrange(1,10)]) #failed attempt 3 print \n.join([%(i)02d_%(j)02d % locals() j=int(8+str(j)) if j6 else int(9+str(j)) for i in xrange(1,20) for j in xrange(1,10)]) Many thanks in advance. Jignesh ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Tutor Digest, Vol 121, Issue 42 nested for
python executes the first for and its condititions then the next for. What i'm saying is that you should first deal with one as nested block codes ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Multiple for and if/else statements into a single list comprehension
Thanks Peter/Denis. I wasn't aware of genexp. I see how you have adapted the code to make it work, I'll adapt the same in my program. Good point about duplicating j , Denis, I guess I was happy to override the outer j as it was intermediate. On 17 March 2014 12:36, spir denis.s...@gmail.com wrote: On 03/17/2014 11:22 AM, Jignesh Sutar wrote: Is it possible to get two nested for statements followed by a nested if/else statement all into a single list comprehension ie. the equivalent of the below: for i in xrange(1,20): for j in xrange(1,10): if j6: j=int(8+str(j)) else: j=int(9+str(j)) print %(i)02d_%(j)02d % locals() You can do it by reformulating your inner block into an expression (here, using a ternary if expression), which will then become the expression part of the comprehension. However, a few remarks: * don't do that: the only advantage is to make your code unreadable * you may reformulate using 2 comprehensions; if you don't want intermediate lists, use a generator expression for the inner one * above, the inner j is a new variable with a distinct meaning: why do you call it j? * do you really need string concat to perform arithmetic? d ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: https://mail.python.org/mailman/listinfo/tutor
