Control Statement

Statement Clause Suite

<header>: #C
	<statement> #S
	<statement>
	... ...
<separating header>:
	<statement>
	<statement>
	... ...

Bool

• False values: False, 0, ”, None
• True values: Anything else
  The outcome of compare is Bool,True or False.

Logical Operators

• and
• or
  Have short-circuit behavior.
  In and If the first number is True, it will return second one, otherwise the first one. By parity of reasoning for or.

Conditional

if Statement

Why we use if statement instead of a call expression? Like this one:

def if_(c,t,f):
	if c:
		return t
	else:
		return f

Because when we call a call expression, it will evaluate all the operands.
But if statement gives us a choice whether to evaluate it or not, avoid some errors.

if_(-4, sqrt(x), 0.0)
#error. Because it evaluate the sqrt(-4) and we just choose the value.

if expression

Put the behavior of if statement on an expression.

<consequent> if <predicate> else <alternative>
 
x if x > 0 else -x # abs(x)
sqrt(x) if x > 0 else 0.0

It is an expression so that it can be used as an argument.

Iteration(Repeating)

while Statement

POINT

• What to follow, or we say, keep track of?

For Statement

It can iterate an iterable value and also Iteration itself.

for <name> in <expression>:  
	<suite>

1. Evaluate the header expression, which must yield an iterable value (a sequence)
2. For each element in that sequence, in order:
   • Bind name to that element in the current frame
   • Execute the suite

Ranges - Another Sequence Type

• Including starting value and excluding the end value range(-2, 2)
• Length: ending value – starting value
• Element selection: starting value + index
• Use a built-in function list to convert it to a list.

 list(range(-2, 2)) # [-2, -1, 0, 1] 
 list(range(4)) # [0, 1, 2, 3]
 """If we just specify one number it will be defaulted to the end value."""

It is not an iterator , range can be call repeatedly, but it is iterable.