Struggling to convert a mysql datetime object to a python string of a different format
python.list at tim.thechases.com
Sat Aug 7 19:12:04 CEST 2010
On 08/07/10 01:45, Νικόλαος Κούρας wrote:
>> # variant B
>> for row in dataset:
>> host, hits, dt = row
>> # rest of your code here
> So, row is a tuple comprising of 3 fields, and host, hist, dt
> are variables assigned each one of row's tuple values by
> breaking it to it's elements.
> But what kind of objects is host, hits, dt that containes the
> row's tuple data themselves? tuples or lists and why?
They contain the data of each respective element. E.g.:
>>> dataset = [
... (1, 'a', True),
... (2, 'b', False),
>>> for one, two, three in dataset:
... print 'one%s = %r' % (type(one), one)
... print 'two%s = %r' % (type(two), two)
... print 'three%s = %r' % (type(three), three)
... print '-' * 10
one<type 'int'> = 1
two<type 'str'> = 'a'
three<type 'bool'> = True
one<type 'int'> = 2
two<type 'str'> = 'b'
three<type 'bool'> = False
So likely in your case, "host" is a string, "hits" is an int, and
"dt" is a datetime.datetime object. The three of them together
are the row as represented as a tuple:
>>> type( (host, hits, dt) )
which you can see in your own code by changing it temporarily to:
for row in dataset:
print type(row), len(row)
>> # variant C
>> for host, hits, dt in row:
>> # rest of your code here
> host, hits, data each and every one of them hold a piece of the row's
> tuple values.
> But what happens in here?
The same as Variant B, only it doesn't use the intermediate tuple
> 'for host, hits, dt in dataset:'
> Here we don't have the row tuple. So what tthose variabels store, and in
> what datatype they strore info in and what is the difference between this
> 'for host, hits, dt in row:'
The second one will fail because it would be the same as
for tpl in row:
host, hits, dt = tpl
The 1st time through the loop, tpl=host; the 2nd time through the
loop, tpl=hits; and the 3rd time through the loop, tpl=dt
Attempting to do a tuple assignment (that 2nd line) will attempt
to do something like
host, hits, dt = "example.com" # 1st pass through the loop
host, hits, dt = 42 # 2nd pass through the loop
host, hits, dt = datetime(2010,7,5)# 3rd pass through the loop
In most cases, it will fail on the first pass through the loop
(except in the freak case your string value happens to have 3
>>> host, hits, dt = "abc" #exactly 3 letters
> If the fieds datatypes returned form the database are for exmaple page
> varchar(50) , hits inteeger, date datetime then
> the when python grabs those results fields it would translate them to
> 'page as string' , (hits as int) , 'date as string' respectively?
> Whcih emans it translated those fileds returned to the most
> appropriate-most close to prototype stored in database' datatypes
Yes, except the internals (of the DB module...in this case mysql)
are smart enough to translate the date into a datetime.datetime
object, instead of a string.
>> row = (host, hits, dt
> Would that be a row or a tuple when joined?
A "row" is a conceptual thing -- one row of data from your query.
It can be represented as either a tuple or a list (or any
iteratable that represents "things in this row"). In this case
(and I believe each row returned by a cursor.fetch*() call), it
I hope that helps...it would behoove you to experiment with
tuple-assignments such as the example code above so that you
understand what it's doing in each case.
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