If Statement in Python (Nested Boolean statements)

Question

I have no Idea if the title uses the correct terms but I am looking to get some code and to try and reduce the length of the code so It will be quicker for me to type in the assessment. Here is and Example of How it would look if I did it the long winded way.

Valid = True
while Valid:
  Column = int(input("Insert Column: "))
  Row = int(input("Insert Row: "))
  if Row < 0 or Row > 9 or Column < 0 or Column > 9:
    Valid = False

However, I was trying to to make that smaller by doing something along the lines of:

"If (Row or Column) < 0 or (Row or Column) > 0:
   valid = False"

Can someone explain why it doesn't seem work and can someone please demonstrate how they would solve it. I am only trying to slim down my if statements since throughout the assessment I will be using a large amount of them.

Update:- Can this also be put into a Try - Catch so it wouldn't crash the program upon entering a Null Value or No value

Thanks

mattsap · Accepted Answer · 2016-05-06 20:44:38Z

4

You can remove the if statement completely.

Valid = True
while Valid:
  try:
     Column = int(input("Insert Column: "))
     Row = int(input("Insert Row: "))
     Valid = Row in range(10)  and Column in range(10)
  except Exception as e:
     print(e)
     Valid = False

edited May 6, 2016 at 20:44

answered May 6, 2016 at 20:19

mattsap

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6 Comments

user2357112 Over a year ago

While this works, I'd advise using a chained comparison 0 <= row < 10 instead of row in range(10), since it behaves better on Python 2 or if you try to use the same construct with floats.

user2357112 Over a year ago

Switching the sense of the test and unconditionally setting Valid is a good move.

itssmegoku Over a year ago

Wouldn't this lead to a true value for valid again?

mattsap Over a year ago

In your example, you set valid to false when it's outside the range. In my code, I set it true when it's inside the range and false when it's outside the range. So it leads to the same answer. My way just has a little less code.

TigerhawkT3 Over a year ago

You might want to catch a specific ValueError rather than Exception.

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TigerhawkT3 · Accepted Answer · 2016-05-06 20:18:35Z

3

The or operator is a short-circuiting comparison that returns the earliest truthy value, or the last value if none are truthy. In (Row or Column) < 0, first Row or Column is evaluated. If Row is nonzero, that section returns Row. Otherwise, it would return Column. It then compares this single value to 0. The same goes for the other comparison, which I assume has a typo and was intended to be (Row or Column) > 9 (rather than > 0).

You can also try the following (not an exhaustive list):

if not 0<=row<=9 or not 0<=column<=9
if row not in range(10) or column not in range(10)
if not all(0<=x<=9 for x in (row,column))

Choose the one that makes the most sense in the context of your program.

answered May 6, 2016 at 20:18

TigerhawkT3

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2 Comments

TigerhawkT3 Over a year ago

@Bahrom - ¯\_(ツ)_/¯

itssmegoku Over a year ago

How would you then adapt this for a Try - Catch Statement

ar-ms · Accepted Answer · 2016-05-06 20:24:03Z

0

You could try this, but this create an array of 10 elements [0..9]..

Valid = True
rangeValue = range(10)
while Valid:
  Column = int(input("Insert Column: "))
  Row = int(input("Insert Row: "))
  Valid = Row in rangeValue and Column in rangeValue

edited May 6, 2016 at 20:24

answered May 6, 2016 at 20:22

ar-ms

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1 Comment

TigerhawkT3 Over a year ago

range() is not inclusive at both ends.

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