If Else Statements in Python | Python for Beginners
Summary
TLDRThis video explains how to use the if-elif-else statement in Python. The instructor demonstrates how to create conditional statements that check whether certain conditions are true or false, using comparison and logical operators. The video walks through writing code for various conditions, including nested if statements and one-line if-else expressions. It also highlights how the Python interpreter evaluates these conditions step-by-step. The guide aims to help viewers understand the structure and flexibility of Python's conditional statements, making it ideal for those learning programming basics.
Takeaways
- 😀 The video covers the if-else statement in Python programming.
- 🤓 The if-else statement evaluates conditions and executes a body of code if true or false.
- 📊 The 'elif' statement checks a secondary condition if the initial 'if' condition is false.
- 🔁 You can have multiple 'elif' statements, but only one 'if' and one 'else' statement in a block.
- 💻 An example was shown where 'if 25 is greater than 10' evaluates as true and prints 'it worked'.
- 🔎 If a condition in 'if' is false, the code moves to the 'else' block for execution.
- 📝 You can chain multiple conditions with 'elif', as demonstrated in the 25, 30, 40, and 50 comparisons.
- ⚙️ Logical operators like 'and' or 'or' can be used inside the condition statements for more complex logic.
- 🚀 Python also allows writing if-else statements in a single line for concise conditions.
- 🧩 Nested if statements are possible, where an if statement is placed within another, allowing more intricate decision-making.
Q & A
What is the basic structure of an if-else statement in Python?
-An if-else statement starts with an 'if' condition. If the condition is true, a block of code is executed. If it's false, the 'else' block of code runs.
What is the purpose of the 'elif' statement in Python?
-'Elif' (short for 'else if') checks another condition if the previous 'if' condition is false. You can have multiple 'elif' statements in a single if-else structure.
How many 'if' and 'else' statements can be used in a Python if-else structure?
-You can only have one 'if' statement and one 'else' statement in a structure, but you can have multiple 'elif' statements between them.
What happens when an 'if' statement's condition is true?
-If the condition is true, Python executes the block of code under the 'if' statement and skips any 'elif' or 'else' blocks.
What happens if all conditions in the if-elif structure are false?
-If all conditions in the 'if' and 'elif' statements are false, the code in the 'else' block is executed.
How does Python handle indentation in if-else statements?
-When writing an if-else statement, Python automatically indents the code inside the body of the statement after a colon (':'). Proper indentation is crucial for defining code blocks.
Can you use multiple comparison operators in an if statement?
-Yes, you can use logical operators like 'and' or 'or' to combine multiple conditions in a single if statement.
How does Python handle a one-line if-else statement?
-Python allows if-else statements to be written on one line using the syntax: 'print(output_if_true) if condition else print(output_if_false)'.
What is a nested if statement?
-A nested if statement is an if statement inside another if statement. It allows for multiple levels of condition checks, creating more complex logic.
What happens when a condition in the elif chain becomes true?
-When a condition in an 'elif' statement becomes true, its corresponding block of code is executed, and the rest of the 'elif' and 'else' statements are skipped.
Outlines
💡 Introduction to the If-Else Statement in Python
The first paragraph introduces the concept of the if-else statement in Python. The speaker explains that while it's technically called the 'if-elif-else' statement, they will refer to it simply as 'if-else'. A blurry flowchart is presented to illustrate how the if statement works. If the initial condition is true, a body of code runs; otherwise, the program moves to the elif condition. If the elif condition is true, another block of code is executed. If both conditions are false, the else statement's code runs. It is emphasized that there can only be one 'if' and one 'else' statement, but multiple 'elif' statements.
🔤 Writing the If-Else Code in Python
In this section, the speaker walks through writing an if-else statement in Python. They start with the 'if' statement, checking if 25 is greater than 10. Since the condition is true, the body of the code prints 'it worked'. Next, the speaker shows how an else statement functions by checking if 25 is less than 10, which is false, leading the program to execute the else block and print 'it did not work'. The process illustrates how Python automatically indents the code for readability, with conditions dictating which block of code is executed.
🧩 Handling Multiple Conditions with Elif
This paragraph introduces the 'elif' statement and shows how it works with multiple conditions. The speaker starts by modifying the previous code to check if 25 is less than 30 using 'elif'. When this condition is true, it prints 'elif worked'. They then demonstrate adding more 'elif' statements with different conditions (25 less than 20, 21, 40, and 50). The first 'elif' condition that evaluates as true (25 < 40) triggers the corresponding code block and prevents the subsequent elifs from running. This section shows how multiple conditions can be evaluated in sequence using 'elif'.
🔗 Using Logical Operators in If Statements
The speaker expands on the use of logical operators like 'and' and 'or' in if statements. By using multiple conditions in one if statement, such as checking whether 25 is less than 10 'or' 1 is less than 3, the code runs if at least one condition is true. They explain how logical operators can combine different conditions to evaluate the truth of an if statement. This section also touches on writing if-else statements in a single line for more concise code, although this approach limits the readability and complexity of the conditions.
🔄 Introducing Nested If Statements
In this part, the speaker explains nested if statements, where one if statement is placed inside another. They demonstrate this by creating a new condition inside an already-true if block. For example, after the first condition (25 < 10 or 1 < 3) is met, they add a nested if statement checking if 10 is greater than 5. If true, it prints another message. This concept allows for more complex decision-making, enabling multiple layers of conditions to be evaluated in sequence. Nested if statements are a powerful tool for advanced logic in Python programming.
📚 Summary and Conclusion
The speaker wraps up the video by summarizing the key points: understanding the basic if-else statement, how to use elif for multiple conditions, using logical operators, and creating nested if statements. They emphasize the flexibility and power of these structures in Python, encouraging viewers to practice writing if-else statements for more complex programming logic. The speaker thanks the audience for watching and encourages them to like and subscribe for more content.
Mindmap
Keywords
💡If Statement
💡Else Statement
💡Elif Statement
💡Condition
💡Logical Operator
💡Comparison Operator
💡Indentation
💡One-Line If Statement
💡Nested If Statement
💡Body of Code
Highlights
Introduction to the if-else statement in Python, explaining its structure and function.
Explanation of the basic if statement: if the condition is true, the code block runs.
Clarification of the elif (else if) statement: checks another condition if the initial if condition is false.
Explanation of the else statement: runs when all previous conditions (if and elif) are false.
Demonstration of a simple if statement: checks if 25 is greater than 10 and prints 'it worked' if true.
Example of an else statement: checks if 25 is less than 10; if false, the else block runs and prints 'it did not work.'
Use of multiple elif conditions: additional elif checks are introduced, demonstrating how they evaluate in sequence.
Illustration of using multiple elif statements: each subsequent elif is evaluated only if all prior conditions are false.
Highlight on the use of logical operators such as 'and' and 'or' within if statements to combine conditions.
Introduction to writing a one-line if-else statement in Python for simpler conditional checks.
Example of a one-line if-else: checks if 10 is greater than 30, prints a result based on the evaluation.
Explanation of nested if statements: placing one if statement inside another to create more complex decision structures.
Demonstration of a nested if statement: checks if 25 is less than 10, and then checks another condition within the first if block.
Emphasis on the flexibility of if-else statements in Python to create highly complex decision-making code.
Final encouragement for understanding if-else logic and nested statements for more advanced Python coding.
Transcripts
hello everybody today we're going to be
taking a look at the if statement within
python now it's actually the if lfl
statement but that's a mouthful so i'm
just going to call it the if else
statement
now we have this flowchart and i
apologize for being blurry but this is
the absolute best one that i could find
right up top we have our if condition
now if this if condition is true we're
going to run a body of code but if that
condition is false we're going to go
over here and go to the lf condition the
lf condition or statement is basically
saying if the first if statement doesn't
work let's try this if statement if this
elf statement is true it goes to this
body of code if it's false it'll come
over here to the else and the else is
basically if all these things don't work
then run this body of code now you can
have as many ill-if statements as you
want but you can only have one if
statement and one else statement so
let's write out some code and see how
this actually looks let's first start
off by writing if that is our if
statement and now we have to write our
condition which is about to be either
met or not met so we'll say if 25 is
greater than 10 which is true
we'll say colon and then we're going to
hit enter and it's going to
automatically indent that line of code
for us and this is our body of code so
if 25 is greater than 10 our body of
code will execute so for us we're just
going to write print and we'll say
it worked
now if we run this it's going to check
is 25 greater than 10 if that is true
print this so let's hit shift enter and
it worked now let's take this exact code
paste it right down here and we'll say
is less than
and right now this if statement is not
true so it's not actually going to work
as you can see there's no output there's
nothing that happened really but it did
check to see if 25 was less than 10 but
it just wasn't true now we can use our
else statement so we're going to come
right down here and we're going to say
else and we'll do a colon and we'll hit
enter again automatically indenting and
we're going to say print
and we're going to say it
did not work
dot dot dot so what it's going to do is
it's going to come up here and check is
25 less than 10
no it's not so this body of code is not
going to be executed it's going to go
right down to this else statement now
this else statement is going to be
printed there's no condition on this so
the if statement has a condition 25 is
less than 10 this has no condition so if
this doesn't work if this is false it's
going to come down here and it will run
this body of code let's run this by
clicking shift enter
and as you can see our output is it did
not work now let's go back up here and
put greater than because this is now
true it's going to say if 25 is greater
than 10 print it worked and then it's
going to stop it's not going to go to
this else statement at all so let's run
this and our output is it worked so what
if we have a lot of different conditions
that we want to try let's come right
down here this is where the elf comes in
so really quickly let's change this to a
not true a false statement we're going
to go down and say alif
and we're going to say
if
it is
and let's say 30
we'll say
lf worked
so now it's going to check is 25 less
than 10 no it's not let's look at the
next condition is 25 less than 30 and if
it is we'll print alif worked so let's
try running this
and alif worked now we can do as many of
these elf statements as we want we can
do
let's just try a few of them right here
so we'll say if 25 is less than 20
is less than 21
and let's do 40
and let's do 50. so we'll say alif lf2
lift 3 and lf4 now if you look at this
the first one that is actually going to
work is this 25 to 40 right here once
this one is checked and it comes out as
true none of the other lf or l
statements will work so let's try this
one it should be lf3
and this one ran properly now within our
condition so far we've only used a
comparison operator we can also use a
logical operator like and or or so we
can say if 25 is less than 10 which it's
not let's say or actually and we'll say
or
one
is less than three which is true if we
run this
now it will actually work so we can use
several different types of operators
within our if statement to see if a
condition is true or not or several
conditions are true there's also a way
to write an if else statement in one
line if you want to do that so we can
write print we'll say it worked
and then we'll come over here and say if
10 is greater than 30 and then we'll
write else
and we'll say
it did not work
just like we had before except now it's
all occurring on one line so let's just
try this and see if it works
so it's saying print it worked if 10 is
greater than 30 which it wasn't so it
went to the else statement and then it
printed out our body right here although
we didn't have any indentation or
multiple lines it was all done in one
line now there's one other thing that we
haven't looked at yet and i'm going to
show it to you really quickly and that's
a nested if statement so when we run
this it's going to say it worked it
works because it says 25 is less than 10
or 1 is less than 3. since this is true
it's going to print out it worked but we
can also do a nested if statement so we
can do multiple if statements as well so
we're going to hit enter and we'll say
if and we'll do a true statement here so
we'll say if 10
is greater than 5 let's do a colon hit
enter and then we'll say print and then
we'll type a string saying this nested
if statement
oops worked
now let's try this out and see what we
get
so it went through the first if
statement it said it was true and it
prints out it worked this is still the
body of code so it goes down to this
next if statement and it says if 10 is
greater than 5 we're going to print this
out and you can do this on and on and on
it can basically go on forever and you
can create a really in-depth logic and
that actually happens a lot when you
start writing more advanced code so i
hope that this was helpful i hope that
you understand the if-else statement
better i hope that you understand how
nested if statements work as well thank
you guys so much for watching if you
like this video be sure to like and
subscribe below and i'll see you in the
next video
[Music]
you
Ver Más Videos Relacionados
5.0 / 5 (0 votes)