You've been looking at simple, sequential issues and
programs so far. To develop more complicated and useful programs, we must offer
our programs the capacity to make decisions based on numerous variables and
modify their behavior accordingly. We must utilize conditional execution for
this.
The simplest form of conditional execution in Python is the
"if" statement.
if time > 12:
print("Good
Afternoon!")
The if statement in Python is fairly simple and obvious. In
Python, the keyword "if" is followed by a logical statement that
returns True or False. You have already studied expressions and variables in
this course. The above example employs a variable called "time" and
utilizes the "greater than" comparison operator to determine whether
the time has passed 12. As illustrated in the example, an if statement always
finishes with a colon.
Under the if statement, the instructions/code to be executed
if the if condition returns True are indented. These indentations are used by
Python to indicate the scope of the if statement. Unlike in many other
programming languages, the leading whitespaces in Python have syntactical
value. There will be more instances of
The visualization of a simple if statement is shown
below.
In the figure above, notice how the program only executes
specific code if the condition returns True. The program does nothing if it
returns False. However, it is frequently beneficial to develop code that
provides an alternate option. We can use an if-else statement to do this.
if time < 12:
print("Good
Morning!")
else:
print("Good
Afternoon!")
The diagram below shows an if - else block. Notice how both
outcomes of the condition are utilized.
The Python "elif" keyword can be used to implement
a multi-way condition. Elif might be thought of as a "else-if". The
software can select one of several pathways by using elifs. The following is
the syntax.
if marks > 80:
print(“A”)
elif 60 <= marks < 80:
print(“B")
elif 50 <= marks < 60:
print("C")
else:
print(“F")
Unlike using several if statements one after the
other, the program evaluates the subsequent elif conditions only if the first
if statement returns False. If any of the successive elif conditions returns
True, we execute that branch and skip over the other elif conditions. The
following is a graphic representation of an if-elif-else block. We don't
examine the conditions that follow if the initial if condition or the
subsequent elif conditions return True.
The best conditional construct for your program is
determined by the solution you use. Visualizing the solution to grasp it before
you begin writing might assist you in selecting the best conditional execution.
As you progress through this course, you will see Try-
except blocks that serve a similar purpose. Exceptions in your code are handled
using try except blocks. They are also known as conditional execution because
they define pathways for the program to pursue if it encounters a problem. More
to come on that later!
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