Python for Data Science

Iterators in Python

Board Infinity
Board Infinity
Iterators in Python

    Python Libraries

    Most important Python Libraries for Data Science

    Arrays In Python

    List vs Tuple: Differences

    List vs Set: Key Differences

    Python List append() Method

    Dictionary of Lists

    Sort Dictionary in Python

    String Comparision in Python

    Zip Function in Python

    Iterators in Python

    Recursion in Python

    with statement in Python

    Python Docstring

    JSON file in Python: Read and Write

    Dictionary to JSON: Conversion in Python

    Beginner's Guide to NumPy in Python

    Numpy in Python

    How to perform Matrix Multiplication with Numpy Python

    What is pandas in python - Pandas Introduction

    Count Rows and Column with Pandas

    How to create an Empty Dataframe in Python using Pandas?

    Pandas append() in Python

    GroupBy Python Function & How To Use It!

    Master Data Visualization using Python

    Python Socket Programming

In python, an object called an iterator is used to iterate over iterable objects such as lists, tuples, dictionaries etc. To initialize this object we need to use the iter() method. For iteration, this object uses the next() method.

iter() method

This method is used for initializing the iterator. This method returns an iterator object.

next() method

For getting the next value of the iterator we use the next() method. While using a loop over an iterable object, it makes use of the iter() object to get an iterable object which after uses the next() function to get the next method to iterate over objects. To signal the end of the iteration it raises a StopIteration signal to do so.

Python iter() example

Code

string = "Hello"
it = iter(string)
print(next(it))
print(next(it))
print(next(it))
print(next(it))
print(next(it))

Output

H
E
L
L
O

Examples

Creating and looping over an iterator using iter() and next()

In the code below, there is a custom iterator that will create an iterator type to iterate over a given limit (from 10 to a certain limit(). Suppose the limit is 13, then it will print 10, 11, 12, and 13. Also if the limit is less than 10, then it will print nothing.

Code

class Test:
    def __init__(self, x):
        self.x = x

    def __iter__(self):
        self.y = 10
        return self
    def __next__(self):
        y = self.y
        if y > self.x:
            raise StopIteration
        self.y = y + 1;
        return y
for no in Test(15):
    print(no)
for no in Test(4):
    print(i)

Output

10
11
12
13
14
15

write your code here: Coding Playground

Iterating over built-in iterables using the iter() method

In the code below, we manage the iterate state and iterator internally, that is we can not see it. We manage t using an object i.e. iterator to traverse over built-in iterable objects such as lists, tuples, dict and sets.

Code

print("Iteration Over List")
l = ["A", "B", "C"]
for i in l:
    print(i)
   
print("\nIteration over Tuple")
t = ("A", "B", "C")
for x in t:
    print(x)
    
print("\nIteration over String")  
s = "Hello"
for S in s :
    print(S)
    
print("\nIteration over Dictionary") 
d = dict()
d['A'] = 1
d['B'] = 2
d['C'] = 3
for D in d :
    print("%s  %d" %(D, d[D]))

Output

Iteration Over List
A
B
C

Iteration over Tuple
A
B
C

Iteration over String
H
e
l
l
o

Iteration over Dictionary
A  1
B  2
C  3

write your code here: Coding Playground

StopIteration Error

While iterating over an iterable object, we can iterate over multiple times, but when all items have iterated successfully it will raise a StopItertaion error.

Code

t = (1, 2, 3, 4)
obj = iter(t)
print("Iterable loop 1:")
for x in t:
    print(x, end=",")
print("\nIterable Loop 2:")
for x in t:
    print(x, end=",")
print("\nIterating on an iterator:")
for x in obj:
    print(x, end=",")
print("\nIterator: Outside loop")
print(next(obj))

Output

Traceback (most recent call last):
  File "<string>", line 17, in <module>
StopIteration

write your code here: Coding Playground