141 lines
4.3 KiB
Markdown
141 lines
4.3 KiB
Markdown
---
|
|
title: If / Elif / Else Statements
|
|
---
|
|
|
|
## If / Elif / Else Statements
|
|
|
|
The `if`/`elif`/`else` structure is a common way to control the flow of a program, allowing you to execute specific blocks of code depending on the value of some data. If the condition following the keyword `if` evaluates as `True`, the block of code will execute:
|
|
|
|
Note that parenthesis are not used before and after the condition check such as in other languages.
|
|
|
|
```python
|
|
if True:
|
|
print('If block will execute!')
|
|
```
|
|
```python
|
|
x = 5
|
|
|
|
if x > 4:
|
|
print("The condition was true!") #this statement executes
|
|
```
|
|
> **Tips** : You can use any number or string or character as alternative to **True** and only **0** and **None** as an alternative to **False**
|
|
|
|
Example:
|
|
```python
|
|
if 1: # 1 evaluates to true
|
|
print('If block will execute!')
|
|
```
|
|
|
|
***Else statement***
|
|
|
|
You can optionally add an `else` response that will execute if the condition is `False`:
|
|
```python
|
|
if not True:
|
|
print('If statement will execute!')
|
|
else:
|
|
print('Else statement will execute!')
|
|
```
|
|
Or you can also see this example:
|
|
```python
|
|
y = 3
|
|
|
|
if y > 4:
|
|
print("I won't print!") #this statement does not execute
|
|
else:
|
|
print("The condition wasn't true!") #this statement executes
|
|
```
|
|
*Note that there is no condition following the `else` keyword - it catches all situations where the condition was `False`*
|
|
|
|
***Elif statement***
|
|
|
|
Multiple conditions can be checked by including one or more `elif` checks after your initial `if` statement but only one condition will execute:
|
|
|
|
```python
|
|
z = 7
|
|
|
|
if z > 8:
|
|
print("I won't print!") #this statement does not execute
|
|
elif z > 5:
|
|
print("I will!") #this statement will execute
|
|
elif z > 6:
|
|
print("I also won't print!") #this statement does not execute
|
|
else:
|
|
print("Neither will I!") #this statement does not execute
|
|
```
|
|
|
|
*Note only the first condition that evaluates as `True` will execute. Even though `z > 6` is `True`, the `if/elif/else` block terminates after the first true condition. This means that an `else` will only execute if none of the conditions prior to it were `True`.*
|
|
|
|
***Nested if statement***
|
|
|
|
We can also create nested `if` statements for decision making. Before preceding, please, refer to the <a href='https://guide.freecodecamp.org/python/code-blocks-and-indentation' target='_blank' rel='nofollow'>indentation guide once</a>.
|
|
|
|
Let's take an example of finding a number which is even and also greater than '10':
|
|
```python
|
|
x = 34
|
|
if x % 2 == 0: # this is how you create a comment and now, checking for even.
|
|
if x > 10:
|
|
print("This number is even and is greater than 10")
|
|
else:
|
|
print("This number is even, but not greater than 10")
|
|
else:
|
|
print ("The number is not even. So no point checking further.")
|
|
```
|
|
Output
|
|
|
|
```python
|
|
This number is even and is greater than 10
|
|
```
|
|
|
|
This was just a simple example of a nested if statement. Please feel free to explore more online.
|
|
|
|
While the examples above are simple, you can create complex conditions using <a href='https://guide.freecodecamp.org/python/comparisons' target='_blank' rel='nofollow'>boolean comparisons</a> and <a href='https://guide.freecodecamp.org/python/boolean-operations' target='_blank' rel='nofollow'>boolean operators</a>.
|
|
|
|
|
|
***Inline python if-else statement***
|
|
|
|
We can also use if-else statements with inline python functions.
|
|
The following example should check if the number is greater or equal than 50, if yes return True:
|
|
|
|
```python
|
|
x = 89
|
|
is_greater = True if x >= 50 else False
|
|
|
|
print(is_greater)
|
|
```
|
|
|
|
Output
|
|
```python
|
|
>
|
|
True
|
|
>
|
|
```
|
|
## Rock-Paper-Scissors Game using if-elif in Python
|
|
|
|
```python
|
|
#importing random library
|
|
import random
|
|
#make the set of moves
|
|
moves = ["rock","paper","scissors"]
|
|
keep_playing = "True"
|
|
|
|
while keep_playing == "True":
|
|
cmove = random.choice(moves)
|
|
pmove = input("What is your move: rock , paper or scissors?")
|
|
print("computer chose ",cmove)
|
|
if cmove == pmove:
|
|
print("Tie")
|
|
elif pmove=="rock" and cmove == "scissors":
|
|
print("player Wins")
|
|
elif pmove == "rock" and cmove == "paper":
|
|
print("computer wins")
|
|
elif pmove == "paper" and cmove =="scissors":
|
|
print("computer wins")
|
|
elif pmove == "paper" and cmove == "rock":
|
|
print ("player wins")
|
|
elif pmove == "scissors" and cmove =="rock":
|
|
print("computter wins")
|
|
elif pmove == "scissors" and cmove =="paper":
|
|
print ("Player wins")
|
|
|
|
```
|