Boolean 'and' in Python

Question

In C# we can do this:

  int i = 5;
  int ii = 10;
  if(i == 5 && ii == 10) {
   Console.WriteLine("i is 5, and ii is 10");

  }
  Console.ReadKey(true);

I tested this in Python:

                 i = 5
                 ii = 10
                 if i == 5 & ii == 10:
                          print "i is 5 and ii is 10";

But this doesn't print out "i is 5 and ii is 10".

What am I doing wrong?

Answer 1

Try this:

i = 5
ii = 10
if i == 5 and ii == 10:
      print "i is 5 and ii is 10"

Edit: Oh, and you dont need that semicolon on the last line (edit to remove it from my code).

Answer 2

& is used for bit-wise comparison. use and instead. and btw, you don't need semicolon at the end of print statement.

Answer 3

The correct operator to be used are the keywords 'or' and 'and', which in your example, the correct way to express this would be:

if i == 5 and ii == 10:
    print "i is 5 and ii is 10"

You can refer the details in the "Boolean Operations" section in the language reference.

Answer 4

You can also test them as a couple.

if (i,ii)==(5,10):
    print "i is 5 and ii is 10"

Answer 5

In python, we spell "&" as "and"

Answer 6

As pointed out, "&" in python performs a bitwise and operation, just as it does in C#. and is the appropriate equivalent to the && operator.

Since we're dealing with booleans (i == 5 is True and ii == 10 is also True), you may wonder why this didn't either work anyway (True being treated as an integer quantity should still mean True & True is a True value), or throw an exception (eg. by forbidding bitwise operations on boolean types)

The reason is operator precedence. The "and" operator binds more loosely than ==, so the expression: "i==5 and ii==10" is equivalent to: "(i==5) and (ii==10)"

However, bitwise & has a higher precedence than "==" (since you wouldn't want expressions like "a & 0xff == ch" to mean "a & (0xff == ch)"), so the expression would actually be interpreted as:

if i == (5 & ii) == 10:

Which is using python's operator chaining to mean: does the valuee of ii anded with 5 equal both i and 10. Obviously this will never be true.

You would actually get (seemingly) the right answer if you had included brackets to force the precedence, so:

if (i==5) & (ii=10)

would cause the statement to be printed. It's the wrong thing to do, however - "&" has many different semantics to "and" - (precedence, short-cirtuiting, behaviour with integer arguments etc), so it's fortunate that you caught this here rather than being fooled till it produced less obvious bugs.