The iter()
function creates an object which can be iterated one element at a time.
These objects are useful when coupled with loops like for loop, while loop.
The syntax of the iter()
function is:
iter(object, sentinel)
iter() Parameters
The iter()
function takes two parameters:
- object - object whose iterator has to be created (can be sets, tuples, etc.)
- sentinel (optional) - special value that is used to represent the end of a sequence
Return value from iter()
- The
iter()
function returns an iterator object for the given object. - If the user-defined object doesn't implement
__iter__()
, and__next__()
or__getitem()__
, theTypeError
exception is raised. - If the sentinel parameter is also provided,
iter()
returns an iterator until the sentinel character isn't found.
Example 1: Working of Python iter()
# list of vowels
vowels = ['a', 'e', 'i', 'o', 'u']
vowels_iter = iter(vowels)
print(next(vowels_iter)) # 'a'
print(next(vowels_iter)) # 'e'
print(next(vowels_iter)) # 'i'
print(next(vowels_iter)) # 'o'
print(next(vowels_iter)) # 'u'
Output
a e i o u
Example 2: iter() for custom objects
class PrintNumber:
def __init__(self, max):
self.max = max
def __iter__(self):
self.num = 0
return self
def __next__(self):
if(self.num >= self.max):
raise StopIteration
self.num += 1
return self.num
print_num = PrintNumber(3)
print_num_iter = iter(print_num)
print(next(print_num_iter)) # 1
print(next(print_num_iter)) # 2
print(next(print_num_iter)) # 3
# raises StopIteration
print(next(print_num_iter))
Output
1 2 3 Traceback (most recent call last): File "", line 23, in File " ", line 11, in __next__ StopIteration
Example 3: iter() with sentinel parameter
class DoubleIt:
def __init__(self):
self.start = 1
def __iter__(self):
return self
def __next__(self):
self.start *= 2
return self.start
__call__ = __next__
my_iter = iter(DoubleIt(), 16)
for x in my_iter:
print(x)
Output
2 4 8
Here, we have implemented a custom iterable object without a StopIteration
condition.
However, we can use the iter()
method with the sentinel
parameter to stop the iteration. If the value returned from __next__()
is equal to sentinel
, StopIteration
will be raised, otherwise, the value will be returned.
Recommended Reading: Python Iterators