In this article, I will show you how to iterate over different types of python objects and get back both the index and the value of each item.<\/p>\n
Jump directly to a specific section:<\/p>\n
- \n
- Enumerate a List<\/a><\/li>\n
- Enumerate a Tuple<\/a><\/li>\n
- Enumerate a List of Tuples (The Neat Way)<\/a><\/li>\n
- Enumerate a String<\/a><\/li>\n
- Enumerate with a Different Starting Index<\/a><\/li>\n
- Why It doesn\u2019t Make Sense to Enumerate Dictionaries and Sets<\/a><\/li>\n
- Advanced: Enumerate Deep Dive<\/a><\/li>\n<\/ul>\n
Enumerate a List<\/h2>\n
Let’s see what to do if we want to enumerate a python list.<\/p>\n
You can iterate over the index and value of an item in a list by using a basic for loop<\/p>\n
L = ['apples', 'bananas', 'oranges']\r\nfor idx, val in enumerate(L):\r\n print(\"index is %d and value is %s\" % (idx, val))<\/code><\/pre>\nThe code above will have this output:<\/p>\n
index is 0 and value is apples\r\nindex is 1 and value is bananas\r\nindex is 2 and value is oranges<\/code><\/pre>\nHow easy was that!<\/p>\n
Now let’s see how to enumerate a tuple.<\/p>\n
Enumerate a Tuple<\/h2>\n
Enumerating a tuple isn’t at all different from enumerating a list.<\/p>\n
t = ('apples', 'bananas', 'oranges')\r\nfor idx, val in enumerate(t):\r\n print(\"index is %d and value is %s\" % (idx, val))<\/code><\/pre>\nAnd as you expect, the output will be:<\/p>\n
index is 0 and value is apples\r\nindex is 1 and value is bananas\r\nindex is 2 and value is oranges<\/code><\/pre>\nNow that you know how to enumerate a list and a tuple, how can you enumerate a list of tuples?\u00a0\ud83e\udd14\ud83e\udd14\ud83e\udd14<\/p>\n
Enumerate a List of Tuples (The Neat Way)<\/h2>\n
Say you have a list of tuples where each tuple is a name-age<\/strong> pair.<\/p>\n
L = [('Matt', 20), ('Karim', 30), ('Maya', 40)]<\/code><\/pre>\nOf course one way to enumerate the list is like this:<\/p>\n
for idx, val in enumerate(L):\r\n name = val[0]\r\n age = val[1]\r\n print(\"index is %d, name is %s, and age is %d\" \\\r\n % (idx, name, age))<\/code><\/pre>\nThe above code will definitely work and it will print out this output.<\/p>\n
index is 0, name is Matt, and age is 20\r\nindex is 1, name is Karim, and age is 30\r\nindex is 2, name is Maya, and age is 40<\/code><\/pre>\nHowever, a cleaner way to achieve this is through\u00a0tuple unpacking<\/strong><\/p>\n
With tuple unpacking, we can do something like this<\/p>\n
for idx, (name, age) in enumerate(L):\r\n print(\"index is %d, name is %s, and age is %d\" \\\r\n % (idx, name, age))<\/code><\/pre>\nEnumerate a String<\/h2>\n
![\"enumerate-string\"](\"http:\/\/www.afternerd.com\/blog\/wp-content\/uploads\/2018\/06\/alphabet.png\")
<\/p>\nSo what happens when you use the enumerate function on a string object?<\/p>\n
An item in a string is a single character.<\/p>\n
So if you enumerate over a string, you will get back the index and value of each character in the string.<\/p>\n
Let’s take an example:<\/p>\n
str = \"Python\"\r\nfor idx, ch in enumerate(str):\r\n print(\"index is %d and character is %s\" \\\r\n % (idx, ch))<\/code><\/pre>\nAnd the output will be:<\/p>\n
index is 0 and character is P\r\nindex is 1 and character is y\r\nindex is 2 and character is t\r\nindex is 3 and character is h\r\nindex is 4 and character is o\r\nindex is 5 and character is n<\/code><\/pre>\nEnumerate with a Different Starting Index<\/h2>\n
So as you know, indices in python start at 0.<\/p>\n
This means that when you use the enumerate<\/strong> function, the index returned for the first item will be 0.<\/p>\n
However, in some cases, you want the loop counter to start at a different number.<\/p>\n
enumerate<\/strong> allows you to do that through an optional start parameter.<\/p>\n
For example, let’s say we want to enumerate over a list starting at 1.<\/p>\n
The code will look like this:<\/p>\n
L = ['apples', 'bananas', 'oranges']\r\nfor idx, s in enumerate(L, start = 1):\r\n print(\"index is %d and value is %s\" \\\r\n % (idx, s))<\/code><\/pre>\nThe above code will result in this output.<\/p>\n
index is 1 and value is apples\r\nindex is 2 and value is bananas\r\nindex is 3 and value is oranges<\/code><\/pre>\nNeedless to say, you can also start with a negative number.<\/p>\n
Why It doesn’t Make Sense to Enumerate Dictionaries and Sets<\/h2>\n
So does it make sense to use the enumerate<\/span> function for dictionaries and sets?<\/p>\n
Absolutely not!<\/strong><\/p>\n
Think about it, the only reason you would use enumerate<\/span> is when you actually care about the index of the item.<\/p>\n
Dictionaries and Sets are not sequences.<\/p>\n
Their items do not have an index, and they don’t, by definition, need one.<\/p>\n
If you want to iterate over the keys and values of a dictionary instead (a very common operation), then you can do that using the following code:<\/p>\n
d = {'a': 1, 'b': 2, 'c': 3}\r\nfor k, v in d.items():\r\n # k is now the key\r\n # v is the value\r\n print(k, v)<\/code><\/pre>\nAnd if you want to iterate over a set, then just use a regular for loop.<\/p>\n
s = {'a', 'b', 'c'}\r\nfor v in s:\r\n print(v)<\/code><\/pre>\nAdvanced: Enumerate Deep Dive<\/h2>\n
In Python, the enumerate<\/span> function returns a Python object of type enumerate<\/span><\/p>\n
Yes, there is an enumerate<\/strong> built-in function and an enumerate<\/strong> object \ud83d\ude42<\/p>\n
>>> type(enumerate([1, 2, 3]))\r\n<class 'enumerate'><\/code><\/pre>\nNow let’s go to Github<\/a> and check how the enumerate<\/strong> object is implemented.<\/p>\n
![\"github-enumerate\"](\"http:\/\/www.afternerd.com\/blog\/wp-content\/uploads\/2018\/06\/Screen-Shot-2018-06-24-at-7.46.07-PM.png\")
<\/p>\nAs you can see, the enumerate<\/span> object stores an index en_index<\/span>, an iterator en_sit<\/span>, and a result tuple en_result<\/span><\/p>\n
en_sit<\/span> is actually the input parameter that we passed to the enumerate<\/strong> function.<\/p>\n
It must be an iterable<\/strong> object.<\/p>\n
At a given index, the result is a tuple of two elements.<\/p>\n
The first element is the index and the second one is the item in en_sit<\/span> with that index.<\/p>\n
enumerate<\/span> objects themselves are also iterables with each item being the mentioned result tuple.<\/p>\n
>>> list(enumerate(['a', 'b', 'c']))\r\n[(0, 'a'), (1, 'b'), (2, 'c')]<\/code><\/pre>\nThat’s why when we iterate over the enumerate object with a for loop like this:<\/p>\n
>>> for idx, val in enumerate(['a', 'b']):\r\n... print(idx, val)\r\n...\r\n0 a\r\n1 b<\/code><\/pre>\nWe are effectively unpacking these tuples to an index and a value.<\/p>\n
But there is nothing that prevents you from doing this (but don’t do it :))<\/p>\n
>>> for i in enumerate(['a', 'b']):\r\n... print(i[0], i[1])\r\n...\r\n0 a\r\n1 b<\/code><\/pre>\nFinally, have fun enumerating \ud83d\ude42<\/p>\n
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