iter() to get iterator from an iterable object in Python

We get an iterator ( output ) from an iterable object ( input ) by using iter function.

iter(iterable_obj,sentinel)

iterable_obj: Required, Object which can be iterated
sentinel: Optional, Value specifying the end of sequence

Example of iterable objects are : List, tuple, dictionary , string

my_str='plus2net'      # a string variable is declared 
my_str=iter(my_str)    # returns an iterator

print(next(my_str))    # p
print(next(my_str))    # l
print(next(my_str))    # u

next() returns the the next item from the iterator Example using one List

my_list=[4,3,5,1]       # declaring a List
my_list1=iter(my_list)  # returns iterator 

print(next(my_list1))   # 4
print(next(my_list1))   # 3
print(next(my_list1))   # 5
print(next(my_list1))   # 1

Type of Iterator

We can check the type of variable we get before and after using iter() function

my_str='plus2net'     # a string variable is declared
print(type(my_str))   # <class 'str'>  
my_str=iter(my_str)   # returns iterator
print(type(my_str))   # <class 'str_iterator'> 

my_list=[4,3,5,1,2]   # declaring a List
print(type(my_list))  # <class 'list'> 
my_list=iter(my_list) # returns iterator
print(type(my_list))  # <class 'list_iterator'>

Exception handling with iter()

What happens if we try to use iter() with a not iterable object as input? We will get TypeError

my_str=4356   # integer variable which is not iterable
my_str=iter(my_str)

Output is here

     my_str=iter(my_str)
TypeError: 'int' object is not iterable

We can use Try Except to handle such error

my_str=4356  # integer variable which is not iterable
try:
    my_str=iter(my_str)
except TypeError as my_msg:
    print ("This is a TypeError")
    print (my_msg)
except:
    print ("Some other error has occured")

Output is here

This is a TypeError
'int' object is not iterable

What happens when there is no item left to return with next() ? We will get StopIteration error

my_str='abc'  
my_str=iter(my_str)
try:
    print(next(my_str))   # a
    print(next(my_str))   # b
    print(next(my_str))   # c
    print(next(my_str))   # Error
except StopIteration:
    print ("This is a StopIteration error")
    
except:
    print ("Some other error has occured")

Output is here

a
b
c
This is a StopIteration error

We can create Iterable object having methods __iter__() and __next__().

class my_iter():

    def __iter__(self):
        self.x=1
        return self

    def __next__(self):
        x=self.x
        self.x=self.x+1
        return x

my_obj=my_iter()
my_iter=iter(my_obj)

print(next(my_iter))  # 1
print(next(my_iter))  # 2
print(next(my_iter))  # 3

We can create StopIteration exception by using raise

class my_iter():

    def __iter__(self):
        self.x=1
        return self

    def __next__(self):
        x=self.x
        self.x=self.x+1
        if(x<5):
         return x
        else:
         raise StopIteration    

my_obj=my_iter()
my_iter=iter(my_obj)

print(next(my_iter))  # 1
print(next(my_iter))  # 2
print(next(my_iter))  # 3
print(next(my_iter))  # 4
print(next(my_iter))  # Error : StopIteration

any() Generator - Tutorials

All String methods list Python- Tutorials

iterator using iter()

Type of Iterator

Exception handling with iter()