fix(guide): move guide to english directory
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Mrugesh Mohapatra
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mrugesh mohapatra
mrugesh mohapatra
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---
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title: For Loop Statements
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---
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## For Loop Statements
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Python utilizes a for loop to iterate over a list of elements. Unlike C or Java, which use the for loop to change a value in steps and access something such as an array using that value.
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For loops iterate over collection based data structures like lists, tuples, and dictionaries.
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The basic syntax is:
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```python
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for value in list_of_values:
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# use value inside this block
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```
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In general, you can use anything as the iterator value, where entries of the iterable can be assigned to. E.g. you can unpack tuples from a list of tuples:
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```python
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list_of_tuples = [(1,2), (3,4)]
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for a, b in list_of_tuples:
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print("a:", a, "b:", b)
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```
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On the other hand, you can loop over anything that is iterable. You can call a function or use a list literal.
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```python
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for person in load_persons():
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print("The name is:", person.name)
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```
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```python
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for character in ["P", "y", "t", "h", "o", "n"]:
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print("Give me a '{}'!".format(character))
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```
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Some ways in which For loops are used:
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**Iterate over the range() function**
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```python
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for i in range(10):
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print(i)
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```
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Rather than being a function, range is actually an immutable sequence type.
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The output will contain results from lower bound i.e 0 to the upper bound i.e 10 but excluding 10.By default the lower bound or the starting index is set to zero.
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Output:
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```
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>
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0
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1
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2
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3
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4
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5
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6
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7
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8
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9
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>
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```
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Additionally, one can specify the lower bound of the sequence and even the step of the sequence by adding a second and a third parameter.
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```python
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for i in range(4,10,2): #From 4 to 9 using a step of two
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print(i)
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```
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Output:
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```
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>
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4
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6
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8
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>
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```
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**xrange() function**
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For the most part, xrange and range are the exact same in terms of functionality. They both provide a way to generate a list of integers for you to use, however you please. The only difference is that range returns a Python list object and xrange returns an xrange object. It means that xrange doesn't actually generate a static list at run-time like range does. It creates the values as you need them with a special technique called yielding. This technique is used with a type of object known as generators.
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One more thing to add. In Python 3.x, the xrange function does not exist anymore. The range function now does what xrange does in Python 2.x
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**Iterate over values in a list or tuple**
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```python
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A = ["hello", 1, 65, "thank you", [2, 3]]
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for value in A:
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print(value)
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```
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Output:
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```
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>
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hello
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1
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65
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thank you
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[2, 3]
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>
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```
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**Iterate over keys in a dictionary (aka hashmap)**
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```python
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fruits_to_colors = {"apple": "#ff0000",
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"lemon": "#ffff00",
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"orange": "#ffa500"}
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for key in fruits_to_colors:
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print(key, fruits_to_colors[key])
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```
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Output:
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```
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>
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apple #ff0000
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lemon #ffff00
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orange #ffa500
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>
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```
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**Iterate over two lists of same size in a single loop with the zip() function**
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```python
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A = ["a", "b", "c"]
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B = ["a", "d", "e"]
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for a, b in zip(A, B):
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print a, b, a == b
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```
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Output:
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```
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>
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a a True
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b d False
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c e False
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>
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```
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**Iterate over a list and get the corresponding index with the enumerate() function**
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```python
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A = ["this", "is", "something", "fun"]
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for index,word in enumerate(A):
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print(index, word)
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```
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Output:
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```
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>
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0 this
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1 is
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2 something
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3 fun
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>
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```
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A common use case is iterating over a dictionary:
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```python
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for name, phonenumber in contacts.items():
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print(name, "is reachable under", phonenumber)
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```
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If you absolutely need to access the current index of your iteration, do **NOT** use `range(len(iterable))`! This is an extremely bad practice and will get you plenty of chuckles from senior Python developers. Use the built in function `enumerate()` instead:
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```python
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for index, item in enumerate(shopping_basket):
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print("Item", index, "is a", item)
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```
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#### More Information:
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- <a href='https://docs.python.org/2.7/tutorial/controlflow.html#for-statements' target='_blank' rel='nofollow'>Python2 for loop documentation</a>
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- <a href='https://docs.python.org/3/tutorial/controlflow.html#for-statements' target='_blank' rel='nofollow'>Python3 for loop documentation</a>
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