List comprehensions are a powerful feature in Python that allows you to construct lists or sequences of values in a concise and readable way. They become even more versatile when you incorporate if-else conditions into them. In this comprehensive guide, we will dive deep into the world of list comprehensions with if-else statements, exploring their syntax, applications, and various methods to make your code more efficient and expressive.

**Understanding List Comprehension Syntax**

List comprehensions in Python follow a specific syntax pattern. They begin with an expression enclosed in square brackets, followed by a for clause. Additional clauses or if-else clauses can follow. The focus here is on if-else clauses within list comprehensions, which provide conditional control.

List comprehensions consist of three main components:

**Expression**: The expression to be evaluated for each item in the iterable.**Iterable**: The sequence of items to iterate over.**Conditional**: An optional condition that filters the items to be included in the resulting list.

## 1) **List Comprehension with If-Else**

When dealing with if-else conditions in list comprehensions, the syntax becomes slightly more complex:

`[expression1(item) if conditional1 else expression2(item) for item in iterable]`

Here’s a breakdown of the components:

**expression1**: The expression to be evaluated if the condition (`conditional1`

) is`True`

.**conditional1**: The condition that determines whether to use`expression1`

or`expression2`

.**expression2**: The expression to be evaluated if the condition (`conditional1`

) is`False`

.**item**: The current item being processed in the iterable.

Let’s create a list of patterns using if-else conditions:

```
pythonCopy codepattern = ["*" if i % 2 == 0 else "+" for i in range(6)]
print('Pattern:\n', pattern)
```

```
Ouput:
Pattern:
['*', '+', '*', '+', '*', '+']
```

In this example, we generate a pattern where even indices in the list receive `'*'`

, and odd indices receive `'+'`

.

### 2) List Comprehension with Only If Clause

If you only need to filter items based on a condition without an else clause, the syntax simplifies:

`[item for item in iterable if conditional]`

Let’s create a list of multiples of 5 using only the if clause:

```
a = [k for k in range(11) if k % 5 == 0]
print('Table of 5:\n', a)
```

```
OUTPUT:
Table of 5:
[0, 5, 10]
```

In this example, we filter the numbers that are multiples of 5 from the range.

## 3) **List Comprehension with Nested If Statements**

List comprehensions can also handle multiple if conditions. For instance, we can create a list of even numbers that are multiples of 4:

```
a = [k for k in range(30) if k % 2 == 0 if k % 4 == 0]
print(a)
```

```
OUTPUT:
[0, 12, 24]
```

This example demonstrates filtering based on multiple conditions, only including numbers that are both even and multiples of 4.

## 4) **List comprehension using if-else with join() function**

List comprehension using if-else condition in aggregation with join() and range() functions.

```
#using list comprehension with join() function
#this will print the pattern upto 5 counts
ifelse=(['*'*i if i else '*' for i in range(6)])
print('pattern: \n',ifelse)
#bound the list to print all pattern
```

```
pattern:
['*', '*', '**', '***', '****', '*****']
```

### 5) **Print the pattern at that iterator at index 5**

```
#using list comprehension with join() function
#this will print the pattern upto 5 counts
ifelse=(['*'*i if i else '*' for i in range(6)])
print('pattern: \n',ifelse[5])
#bound the list to print pattern which iterate over the index 5
```

```
pattern:
*****
```

## 6) **list comprehension using if statement in Python**

The syntax of using if statement using list comprehension

```
a = ([k for k in range(21) if (k%2==0)])
print('table of 2: \n', a)
```

```
table of 2:
[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]
```

Performing the above operation without if-else conditions using list comprehension.

`[j*k for k in range(0,11) for j in range(2,3)]`

`[0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20]`

## 7) **list comprehension using nested if statements in Python.**

Condition: only *even* numbers that are multiples of 4 will be added to the list ‘a’.

List= [item for item in iterable if condition == True]

```
#using muliple if
a = [k for k in range(30) if k%2==0 if k%3==0 if k%4==0]
print(a)
```

`[0, 12, 24]`

## 8) **list comprehension with if else in Python.**

[expression if condition1 else condition2 for item in iterable]

```
pattern = ["*" if i%2==0 else "+" for i in range(6)]
print('pattern: \n', pattern)
```

```
pattern:
['*', '+', '*', '+', '*', '+']
```

**In a list comprehension, there are two things to consider when using if/else statements:**

**List comprehensions****Conditional Operators**

In the Following Example, there will be no additions or updates to the list except for even numbers.

```
new_list = [expression for item in iterable if condition == True]
if_ = [k for k in range(0, 41) if k % 4 == 0]
if_
```

`[0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40]`

## 9) **List Comprehensions with Conditionals**

Condition: *even* numbers will be added as **‘+’**, the number 5 will be added as ‘***’ and the odd will be added as **‘-’.**

```
a = ['+' if k % 2 == 0 else '***' if k == 5 else '-' for k in range(0, 15)]
a
#print '+' for even, and '-' for old, and for number 5 it print pattern
```

`['+', '-', '+', '-', '+', '***', '+', '-', '+', '-', '+', '-', '+', '-', '+']`

Among other things, this example checks to see if the number n is even (that is, if n is divisible by 2 without remainder). New lists include the string “+” if it is true; otherwise, it includes “-“, and at number n=5, it returns a pattern.

### 10) **List Comprehensions with if-else Conditionals**

In the following example, a list comprehension search and match the results with if-else clauses. However, **if the number n is even **(that is, if k is divisible by 2 without remainder), then New lists include the string “+” if the number is even; else wise, it updates the list with the string “-” for the odd number.

```
List=[0, 3, 4, 8, 12, 16, 19, 20, 24, 28, 31, 32, 36, 40, 41]
plus_min = ["+" if k % 2 == 0 else "-" for k in List]
print(plus_min)
```

`['+', '-', '+', '+', '+', '+', '-', '+', '+', '+', '-', '+', '+', '+', '-']`

### 11) **Comparison case of list comprehension using if else**

```
a= (", ".join(["*" if k else "**" for k in range(3)]))
print(a, type(a))
```

`**, *, * <class 'str'>`

```
a= ["*" if k else "**" for k in range(3)]
print(a, type(a))
```

```
['**', '*', '*'] <class 'list'>
```

In Case:1 and Case:2, When 0 is generated by the function range(), if k generates **False (execute else statement and print (**))**. Otherwise, it yields to **True and print ‘*’**. However, join() function returns the list comprehension in String data-type. And in Case:2, the returns list.

**Conclusion**

List comprehensions in Python provide a concise and efficient way to create lists with conditional logic. In this comprehensive guide, you’ve learned how to use if-else conditions, nested if statements, and filter items based on various conditions. Remember that the `for...in`

structure should always come at the end of the list comprehension syntax when handling if-else conditional clauses.

To further enhance your Python programming skills, consider exploring additional Python programming tutorials. Happy coding!