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Python foreach equivalent


Question

I am diving into Python and I have a question about foreach iteration. I am new to Python and I have some experience in C#. So I am wondering, if there is some equivalent function in Python for iteration all over all items in my collection, e.g.

pets = ['cat', 'dog', 'fish']
marks = [ 5, 4, 3, 2, 1]

or something like this.

2016/10/31
1
197
10/31/2016 4:37:53 PM

Accepted Answer

Sure. A for loop.

for f in pets:
    print f
2016/10/31
300
10/31/2016 4:36:00 PM

Like this:

for pet in pets :
  print(pet)

In fact, Python only has foreach style for loops.

2016/10/31

Its also interesting to observe this

To iterate over the indices of a sequence, you can combine range() and len() as follows:

a = ['Mary', 'had', 'a', 'little', 'lamb']
for i in range(len(a)):
  print(i, a[i])

output

0 Mary
1 had
2 a
3 little
4 lamb

Edit#1: Alternate way:

When looping through a sequence, the position index and corresponding value can be retrieved at the same time using the enumerate() function.

for i, v in enumerate(['tic', 'tac', 'toe']):
  print(i, v)

output

0 tic
1 tac
2 toe
2018/05/20

For an updated answer you can build a forEach function in Python easily:

def forEach(list, function):
    for i, v in enumerate(list):
        function(v, i, list)

You could also adapt this to map, reduce, filter, and any other array functions from other languages or precedence you'd want to bring over. For loops are fast enough, but the boiler plate is longer than forEach or the other functions. You could also extend list to have these functions with a local pointer to a class so you could call them directly on lists as well.

2020/07/09

While the answers above are valid, if you are iterating over a dict {key:value} it this is the approach I like to use:

for key, value in Dictionary.items():
    print(key, value)

Therefore, if I wanted to do something like stringify all keys and values in my dictionary, I would do this:

stringified_dictionary = {}
for key, value in Dictionary.items():
    stringified_dictionary.update({str(key): str(value)})
return stringified_dictionary

This avoids any mutation issues when applying this type of iteration, which can cause erratic behavior (sometimes) in my experience.

2018/08/28

For a dict we can use a for loop to iterate through the index, key and value:

dictionary = {'a': 0, 'z': 25}
for index, (key, value) in enumerate(dictionary.items()):
     ## Code here ##
2018/11/01