Do You Need A Foreach in Python? [Alternatives]

Java 5 introduced the foreach method for iterating arrays similarly to the for loop, while loop, and do-while loop. Unfortunately, there is no exact foreach keyword in Python. There are different ways through which you can use it.

Like a normal for-loop, it begins with the keyword for. Rather than declaring and initializing loop counter variables, you declare a variable with the same type as the array, followed by a colon and then the array name. You can use your loop variable instead of an indexed array element in the loop body.

What’s the Difference between For and Foreach Loop?

For LoopForeach Loop
The most traditional way of iterating over arraysA modern approach to iterating over sequence data types.
It does not pass any call-back functions while iterating.The foreach loop passes a call-back function for each element of an array.
Works with an iterator, counter, and incrementor.Works with the iterator, index of an element, and sequence type to iterate through.

Is there a foreach looping statement in Python?

As of Python 3.10, there isn’t a dedicated foreach syntax available. The standard Python for loop has similar functionality to a so-called “foreach loop”. Look at the below example:

for item in sequence:
     print(item)

The above loop iterates through each “item” in the sequence structure. On every iteration, the loop performs a print operation on the “item”. This, as you can see, is very similar to a Foreach statement in Java. A call-back, in this case – print, is being requested.

Writing a User Defined Foreach loop in Python

The following example shows how a standard foreach loop works. You can try this implementation on your browser here.

def myForEach(aFunction, anIterable):
    for eachElement in anIterable:
        aFunction(eachElement)

Explanation:

myForEach Is a function that takes 2 arguments. One is a function to allow call-backs for each eachElement. The other is a sequence data or an iterable type. Upon each iteration, a call back is performed aFunction on each item in the iterable.

Writing a Traditional For Loop in Python

The example below illustrates how traditional for-loops work.

myArray = ['a', 'b', 'c']
for index in range(len(myArray)):
    print("index: %s | value: %s" % (index, myArray[index]))

Output

index: 0 | value: a
index: 1 | value: b
index: 2 | value: c

Explanation:

We iterate through the array myArray consisting of 3 elements in our “for loop”. Instead of iterating through the array itself, we’re keeping track of the index values. The iterations proceed till the end of the array. Unlike the foreach loop, the for loop iterates based on the size of the iterable and keeps track of the index position.

Iterating Through a Dictionary in Python using foreach

For dictionaries and mappings, __iter()__ is used to iterate over keys. In other words, if you directly put a dictionary into a for loop, Python will automatically call __iter()__ on that dictionary, giving you an iterator over its keys.

Python understands that a_dict is a dictionary and that it implements __iter()__.

myDict = {'color': 'blue', 'fruit': 'apple', 'pet': 'dog'}
for key in myDict:
     print(key)

Upon each iteration, the loop is making a call-back to the “print” function.

Parallelizing the for loop In Python

Using Python’s multiprocessing package, we can send a request to another process and create a child process, parallelizing the loop. For each element of the iterable, the multiprocessing module could be substituted for the for loop. Due to the Global Interpreter Lock, using multiple threads in Python would not provide better results. multiprocessing.pool() function can be used. Refer to the following implementation:

import multiprocessing

def sumAll(value):
    return sum(range(1, value + 1))

pool_obj = multiprocessing.Pool()

result = pool_obj.map(sumAll,range(0,5))
print(result)

Output

0, 1, 3, 6, 10

Foreach Loops Using Django Templates

A Django template is a text document or a Python string mark-up using the Django template language. These templates allow data from viewable to the template and provide features of programming such as variables, loops, and comments.

Here’s the Django template syntax for a for loop.

{% for i in iterable %}
{% endfor %}

Actual implementation:

<ul>
{% for Item in MyDict %}
    <li>{{ MyDict.value}}</li>
{% endfor %}
</ul>

Skipping the First or Last Element Using Python For Loop

To skip the first element in an iterable, pass:

for item in myIterable[1:]:
     print(item)

Similarly, to skip the last element:

for item in myIterable[:-1]:
     print(item)

FAQs on Python Foreach

How is Python Foreach better than the standard for loop?

foreach loops are usually faster┬ábecause the local variable that stores the element’s value in the array is faster to access than an element in the array. However, the for loop can be more efficient if the iterable has to be accessed every iteration.

Why Python doesn’t require foreach?

As discussed, Python’s for-loop has behaviors similar to a standard foreach loop. Python for loop iterates through each “item” in the sequence structure. On every iteration, the loop performs a print operation on the “item”. Thereby functioning similarly to a traditional foreach.

Conclusion

We have discussed the foreach loop and its relevancy in Python 3. The differences between the classic for and for each loop have been established. We have also discussed how the Python for loop behaves like a foreach loop in functionality.

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