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
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