How to convert a list of integers to an integer by multiplying all values in a Python list? You can convert a list of integers into a single integer using many ways, for example, by using the `for` loop, list comprehension, `reduce()` method with an `lambda` expression, and `map()` with `join()` functions. In this article, I will explain how to convert a list to an integer by using all these methods with examples.

1. Quick Examples of List to Integer

If you are in a hurry, below are some quick examples of converting a list into an integer.

``````
# Quick examples of convert list to integer

# Initialize list
mylist = [3, 6, 5, 8]

# Example 1: Using for loop
number = 0
for digit in mylist:
number = number*10 + digit

# Example 2: Convert list to integer
# Using list comprehension
number = int(''.join(str(digit) for digit in mylist))

# Example 3: Using list comprehension
new_list = [str(digit) for digit in mylist]
string_value = "".join(new_list)
number = int(string_value)

# Example 4: Using the reduce() method
# With lambda expression
number = reduce(lambda x, y: x * 10 + y, mylist)

# Example 5: Convert list to integer
# Using map() and join() methods
number = int(''.join(map(str, mylist)))

# Example 6: Using map() and join() methods
new_list = map(str, mylist)
string_value = ''.join(new_list)
number = int(string_value)
``````

2. Convert List to Integer Using For Loop

You can convert a list to an integer using a for loop, you can iterate over the list of elements and build the integer step by step.

For example, you can start with an initial number of `0`. Then, for each digit in the list, you can multiply the current number by `10 `(to shift the previous digits to the left) and add the current digit. This process continues until you iterate over all the `mylist` in the list, resulting in the complete integer. You can replace the `mylist` list with your own list of digits to convert it into an integer using a similar approach.

Here are the iterations for the conversion of the list `[3,6,5,8]` to an integer.

• number = 0*10+3 = 3
• number = 3*10+6 = 36
• number = 36*10+5 =365
• number = 365*10+8 = 3658
``````
# Initialize list
mylist = [3, 6, 5, 8]
print("Original list: ",mylist)

# Using for loop to convert list to int
number = 0
for digit in mylist:
number = number*10 + digit
print("After converting the list to an integer:",number)
``````

Yields below output.

3. Convert List to Integer Using List Comprehension

You can also use list comprehension to convert the list to an integer. You can join the list(`mylist`) together as strings and then convert the resulting string to an integer.

In the below example, the `str(digit) `part converts each digit in the list to a string. Then, `''.join() `joins all the individual strings together with an empty string as the separator. Finally,` int()` is used to convert the resulting string to an integer.

``````
# Initialize list
mylist = [3, 6, 5, 8]
print("Original list: ",mylist)

# Convert list to integer
# Using list comprehension
number = int(''.join(str(digit) for digit in mylist))
print("After converting the list to an integer:",number)

# Using list comprehension
new_list = [str(digit) for digit in mylist]
string_value = "".join(new_list)
number = int(string_value)
print("After converting the list to an integer:",number)
``````

Yields the same output as above.

4. Using the reduce() Method with Lambda Expression

Alternatively, You can use reduce() method from the `functools` module with a lambda expression to convert the list into an integer. Simply you can perform a series of calculations to combine the digits. For example, you can import the `reduce()` function from the `functools` module. This function takes two arguments, the lambda expression and the list of digits. The lambda expression takes two inputs, `x` and `y`, and performs the calculation `x*10+y` to combine the digits.

The `reduce()` function applies the `lambda expression` to the list of digits in a cumulative manner, starting from the left. This process combines the digits step by step until a single integer result is obtained.

``````
from functools import reduce

# Initialize list
mylist = [3, 6, 5, 8]
print("Original list: ",mylist)

# Using the reduce() method with lambda expression
number = reduce(lambda x, y: x * 10 + y, mylist)
print("After converting the list to an integer:",number)
``````

Yields the same output as above.

5. Using map() and join() Methods

You can also use map() and `join()` methods to convert the list into an integer. First, you can apply to map each digit to a string, then join the strings together, and finally convert the resulting string to an integer.

In the below example, the `map(str, mylist)` part applies the `str()` function to each digit in the list, converting them into strings. The `join()` method then concatenates these strings together with an empty string as the separator. Finally, `int()` is used to convert the resulting string to an integer.

``````
# Initialize list
mylist = [3, 6, 5, 8]
print("Original list: ",mylist)

# Convert list to integer
# Using map() and join() methods
number = int(''.join(map(str, mylist)))
print("After converting the list to an integer:",number)

# Using map() and join() methods
new_list = map(str, mylist)
string_value = ''.join(new_list)
number = int(string_value)
print("After converting the list to an integer:",number)
``````

Yields the same output as above.

Conclusion

In this article, I have explained how to convert a list to an integer in Python by using `for` loop, list comprehension, `reduce() `method with `lambda` expression, and map() & join() functions with examples.

Happy Learning !!