KJZZ Webmaster wrote:
> I have a list of dictionaries. Each dictionary has a key named "program".
>
> I can display a html table for the entire list of dictionaries, however...
>
> I would like to display distinct html tables for each program while also
> displaying the playlist for the day in chronological order (the list has
> already been sorted according to time).
>
> One note: If a program starts at midnight and ends at 3am. Then starts
> again at 11pm and goes to midnight, it should be displayed in two tables at
> both the start and the end of the playlist for the day.
You need to make two changes - put the table generation in a loop, and
group the records by program. The looping part is pretty simple, the
grouping can be done by itertools.groupby(). I owe the list an
explanation of groupby() so let me try it.
Suppose you have a list of dicts containing the names of cities and
states, and you want to print them out with headings by state:
>>> cities = [
... { 'city' : 'Harford', 'state' : 'Connecticut' },
... { 'city' : 'Boston', 'state' : 'Massachusetts' },
... { 'city' : 'Worcester', 'state' : 'Massachusetts' },
... { 'city' : 'Albany', 'state' : 'New York' },
... { 'city' : 'New York City', 'state' : 'New York' },
... { 'city' : 'Yonkers', 'state' : 'New York' },
... ]
First let me explain operator.itemgetter(). This function is a factory
for new functions. It creates functions that access items using a key.
In this case I will use it to create a function to access the 'state'
item of each record:
>>> from operator import itemgetter
>>> getState = itemgetter('state')
>>> getState
<operator.itemgetter object at 0x00A31D90>
>>> getState(cities[0])
'Connecticut'
>>> [ getState(record) for record in cities ]
['Connecticut', 'Massachusetts', 'Massachusetts', 'New York', 'New
York', 'New York']
So itemgetter('state') is a function that accepts a dict as an argument
and returns the 'state' item of the dict. Calling getState(d) is the
same as writing d['state'].
What does this have to do with groupby?
>>> from itertools import groupby
>>> help(groupby)
Help on class groupby in module itertools:
class groupby(__builtin__.object)
| groupby(iterable[, keyfunc]) -> create an iterator which returns
| (key, sub-iterator) grouped by each value of key(value).
groupby() takes an optional second argument which is a function to
extract keys from the data. getState() is just the function we need.
>>> groups = groupby(cities, getState)
>>> groups
<itertools.groupby object at 0x00A88300>
Hmm. That's a bit opaque. groupby() returns an iterator. Each item in
the iterator is a pair of (key, group). Let's take a look:
>>> for key, group in groups:
... print key, group
...
Connecticut <itertools._grouper object at 0x0089D0F0>
Massachusetts <itertools._grouper object at 0x0089D0C0>
New York <itertools._grouper object at 0x0089D0F0>
Hmm. Still a bit opaque :-) The 'key' part is clear - that's the state,
extracted with the itemgetter getState - but the group is _another_
iterator. One way to look at it's contents is to use a nested loop. Note
that I have to call groupby again, the old iterator was consumed by the
last loop:
>>> for key, group in groupby(cities, getState):
... print key
... for record in group:
... print record
...
Connecticut
{'city': 'Harford', 'state': 'Connecticut'}
Massachusetts
{'city': 'Boston', 'state': 'Massachusetts'}
{'city': 'Worcester', 'state': 'Massachusetts'}
New York
{'city': 'Albany', 'state': 'New York'}
{'city': 'New York City', 'state': 'New York'}
{'city': 'Yonkers', 'state': 'New York'}
Well that makes more sense! And it's not too far from the original
requirement, we just need to pretty up the output a bit. How about this:
>>> for key, group in groupby(cities, getState):
... print 'State:', key
... for record in group:
... print ' ', record['city']
...
State: Connecticut
Harford
State: Massachusetts
Boston
Worcester
State: New York
Albany
New York City
Yonkers
Other than misspelling Hartford (sheesh, and I grew up in Connecticut!)
that's not too bad!
In your case, the output is more complex so you probably want to make
some functions to break it into smaller pieces, but the overall idea
should work for you.
Kent
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