Stefan Ram wrote:
"ROGER GRAYDON CHRISTMAN" <d...@psu.edu> writes:
On Wed, Oct 4, 2017 22:42 Stefan Ram (r...@zedat.fu-berlin.de) wrote:
Steve D'Aprano <steve+pyt...@pearwood.info> writes:
So, "bottom-up" in this case means: iterators should be
taught before for-loops.
Why?
The easy answer here is to not use the range in the first for loop.
I never intended to use »range«. But I also will not use lists.
Very early in the course, I teach numeric and string literals:
1, 2.3, 'abc'
then come operators, functions and »if«, »while« and »try«.
But neither »range« nor lists have been shown so far.
As long as I have two teachers here, which textbooks are you using? I am
hoping to teach a college course in Python next fall.
Thanks,
Bill
The basic course may already and there after about 12 - 18 hours.
(This time includes many exercises in the classroom.)
But if I have time to introduce »for«, I'll do it as follows
at this point in the course:
<now speaking like a teacher:>
We want to walk through (traverse) a string
character-by-character:
To do this we need a walker. A walker can be
obtained using »iter«:
|>>> walker = iter( 'abc' )
Now, we can get character after character from the walker
using »next« (transcript simplified):
|>>> next( walker )
|'a'
|>>> next( walker )
|'b'
|>>> next( walker )
|'c'
|>>> next( walker )
|StopIteration
We can use »while« to automate this:
def example():
walker = iter( 'abc' )
try:
while True:
print( next( walker ))
except StopIteration:
pass
A walker also is known as an /iterator/.
An object, one can get an iterator from
is called an /iterable object/.
Strings are iterable objects.
This for-loop does just what our previous
while-loop did:
def example():
for ch in 'abc':
print( ch )
It gets an iterator from »'abc'« and then does the suite
repeatedly with »ch« being the result of a each »next«
call until StopIteration.
</end of "speaking like a teacher">
No »range«, no list.
(Yes, »print('\n'.join('abc'))« can do the same and will
be shown later in the course if there is still time.)
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