Python Syntax for Chained Conditionals

Question

I'm a beginner in Python currently self-learning via the book "How to Think like a Computer Scientist" From an exercise from the book on Chained Conditionals, Syntax taught was:

 def function(x,y)
   if ..:
      print ".."
   elif..:
      print ".."
   else:
      print".."

However, when I tried this to find out if its legal, it worked:

 def function (x,y)
   if ..:
     print ".."
   if ..:
     print ".."

Is the latter a correct syntax? Or is it not even considered a chained conditional? I would like to find out that even if this is legal in Python, is it a "good way" to write the code?

All kind help is sincerely appreciated.

Answer 1

Though your second example is working, it is not the same thing as the first example. In the second, every if condition will be evaluated, regardless of whether or not a previous one was true and executed. In the chained if/elif example, the whole thing is treated as a unit and only the first matched condition will be executed.

For example:

# An if/elif chain
a = 2
b = 3

if a == 2:
  print "a is 2"
elif b == 3:
  print "b is 3"
else:
  print "whatever"

# prints only
"a is 2"
# even though the b condition is also true.

However

# Sequential if statements, not chained
a = 2
b = 3

if a == 2:
  print "a is 2"

if b == 3:
  print "b is 3"

# prints both
"a is 2"
"b is 3"