In the example given for While Loops—
dog_breeds = [‘bulldog’, ‘dalmation’, ‘shihtzu’, ‘poodle’, ‘collie’]
index = 0
while index < len(dog_breeds):
print(dog_breeds[index])
index += 1
What is the purpose of—
index += 1
We need to be sure that i is constantly changing (increasing) so that the test condition eventually fails, otherwise the loop will run indefinitely (infinite loop). We wouldn’t want that.
11 Likes
dog_breeds = [‘bulldog’, ‘dalmation’, ‘shihtzu’, ‘poodle’, ‘collie’]
for dog_breeds
i got an error is If i used a single ’ quote.
it work with " double quote.
Sorry I still dont get this can you elaborate a bit further please.
1 Like
Every loop needs to stop at some point, for this example it is going to happen when index exceeds.
index =+ 1 means, index = index + 1.
If we want to reach that point we need to bring the ‘index’ value to that level by adding 1 in every iteration by index =+ 1.
3 Likes
so we can write it both ways? i+=1 and i=+1
The one on the left, only. The assignment operator (=) must be last, always.
4 Likes
Even when this is available on other programming languages like C, C++. Python only allows the i += 1
1 Like
You can also use the syntax i=i+1
This code seems to work fine:
while len(students_in_poetry) < 6:
name = all_students.pop()
students_in_poetry.append(name)
Was I supposed to count index in this exercise?
ps. first time posting - couldn’t figure out how to make indented text in the post… sorry…
No, since we are tracking the length of the students_in_poetry list.
I guess i++ should also work.
Not in Python. We don’t have those unary operators at our disposal.
2 Likes
If a loop is designed to iterate an operation across a list, index by index starting from 0, why do we need to include notation that tells it to increase the index? I guess I figured the (index += 1) was implied by the loop itself. When would I need to vs. not need to specify this condition in my code?
Python iterable objects have a method for iterating them. A range is an iterable object. The method is a property of that object and works in the background. We don’t need to increment the index the way we do in JavaScript, etc.
>>> a = range(10)
>>> dir(a)
['__bool__', '__class__', '__contains__', '__delattr__',
'__dir__', '__doc__', '__eq__', '__format__', '__ge__',
'__getattribute__', '__getitem__', '__gt__', '__hash__',
'__init__', '__init_subclass__', '__iter__', '__le__',
'__len__', '__lt__', '__ne__', '__new__', '__reduce__',
'__reduce_ex__', '__repr__', '__reversed__', '__setattr__',
'__sizeof__', '__str__', '__subclasshook__', 'count',
'index', 'start', 'step', 'stop']
>>>
Note the dunder method, above… __iter__. That’s the method that is running in the background. for calls that method on the range.
So everytime it loops index is increased by 1?
Correct.
The code inside a loop will run each time the loop iterates, unless you have a break, continue, or return statement; conditional statements; etc.
Thank you, my brain tells me to do this: 1 + index = index… but that doesn’t seem right either haha
You’re correct in that this is incorrect. When assigning variables values, the expression on the right side of the assignment operator (=) is evaluated, then assigned to the variable on the left. Here, you are trying to assign 1 + index the value of index. 1 + index is not a valid variable name and will throw an error. You’re nearly there though!
You see what they mean by how weird this appears on first glance?
a = a + 1
The reverse can never be true.
a + 1 = a
The complexity of the mind is something we must always be wary of. IT sees these anomalies long before we do.