Iterator does not return self from __iter__ method¶
ID: py/iter-returns-non-self
Kind: problem
Security severity:
Severity: error
Precision: high
Tags:
- reliability
- correctness
Query suites:
- python-security-and-quality.qls
Click to see the query in the CodeQL repository
The __iter__ method of an iterator should return self. This is important so that iterators can be used as sequences in any context that expect a sequence. To do so requires that __iter__ is idempotent on iterators.
Note that sequences and mapping should return a new iterator, it is just the returned iterator that must obey this constraint.
Recommendation¶
Make the __iter__ return self unless the class should not be an iterator, in which case rename the next (Python 2) or __next__ (Python 3) to something else.
Example¶
In this example the Counter class’s __iter__ method does not return self (or even an iterator). This will cause the program to fail when anyone attempts to use the iterator in a for loop or in statement.
class MyRange(object):
def __init__(self, low, high):
self.current = low
self.high = high
def __iter__(self):
return self.current
def next(self):
if self.current > self.high:
raise StopIteration
self.current += 1
return self.current - 1
References¶
Python Language Reference: object.iter.
Python Standard Library: Iterators.