On 24Mar2019 14:33, boB Stepp <robertvst...@gmail.com> wrote:
On 23Mar2019 22:15, boB Stepp <robertvst...@gmail.com> wrote:
The lambda is just a single line function definition, and doesn't get a
function name.
So your get_input name now accepts a "date_constructor" parameter and
you would change the input step from this:
try:
identifier = int(input(input_prompt))
if date_value_err_ck:
date(*date_value_err_ck)
except ValueError:
to this:
try:
value = int(input(input_prompt))
date = date_constructor(value)
except ValueError:
You could not know this from the code I showed (As I pared it down to
illustrate my problem.), but I am also using get_input() to pull in
from the user non-date values, too, but they are also all integers:
pages_read and total_pages_to_read. Because of this, for these latter
two items, "date_value_err_ck" will be assigned "None", which is why I
have the "if date_value_err_ck:".
Ok. So I realised later that you're not using the date from
date_constructor; you're just calling it to see if it raises ValueError
as a sanity check.
Why not make that a condition, and drop date_value_err_ck altogether?
'conditions': [
(lambda goal_year: datetime.date(goal_year, 1, 1),
"This doesn't look like a valid date year to datetime.date()."),
and make the condition checking code more robust:
for bad_condition, message in conditions:
try:
badness = bad_condition(input_value)
except ValueError as e:
print("Invalid goal_year, cannot even run the condition check! " +
str(e))
else:
if badness:
print(message)
That reduces your opening try/except to just checking that the input is
a valid int, a lot simpler.
Well, when you define the goal_month constructor lambda function,
goal_year _is_ a local variable. And _because_ it is not a parameter of
the lambda, the lambda finds it in the scope where it was defined: the
scope at the bottom of your programme.
This is called a "closure": functions has access to the scope they are
define in for identifiers not locally defined (eg in the parameters or
the function local variables - which are those assigned to in the code).
This is so cool and useful! I recall seeing this mentioned for nested
functions, but did not know it worked for lambdas as well.
Lambda are functions. Same rules.
Cheers,
Cameron Simpson <c...@cskk.id.au>
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