Code suggestion - List comprehension

Peter Otten __peter__ at web.de
Fri Dec 13 10:43:37 CET 2013


Shyam Parimal Katti wrote:

> Hello,
> 
> I have a list of sql queries, some which are split across multiple list
> elements e.x.
> ['drop table sample_table;', 'create table sample_test', '(col1 int);',
> 'select col1 from', ' sample_test;']
> 
> A semi-colon in the string value  indicates the termination of a sql
> query. So the expected out come is a conversion to a list of valid sql
> queries:
> ['drop table sample_table;', 'create table sample_test (col1 int);',
> 'select col1 from sample_test;']
> 
> Here is the code that does that:
> 
> sample = ['drop table sample_table;', 'create table sample_test', '(col1
> int);', 'select col1 from', ' sample_test;']
> pure_sqls = []
> query_holder= ''
> for each_line in sample:
>     query_holder += each_line
>     if query_holder.endswith(';'):
>         pure_sqls.append(query_holder)
>         query_holder = ''
> 
> 
> Is there a way to do this by eliminating explicit creation of new
> list(pure_sqls) and a temporary variable(query_holder)? Using list
> comprehension? Though I don't want to put the shorter version in
> production(if it is difficult to understand), I am looking if this can be
> done with list comprehension since I am trying to learn list comprehension
> by using it in such scenarios.

Yours is the sane approach, but it may be fun to try to understand the 
following evil hacks ;)

>>> [sql.replace("\0", " ") + ";" for sql in "\0".join(sample + 
[""]).split(";\0") if sql]
['drop table sample_table;', 'create table sample_test (col1 int);', 'select 
col1 from  sample_test;']


>>> from itertools import groupby
>>> def key(x, group=[0]):
...     try:
...             return group[0]
...     finally:
...             group[0] += x.endswith(";")
... 
>>> [" ".join(group) for _, group in groupby(sample, key)]
['drop table sample_table;', 'create table sample_test (col1 int);', 'select 
col1 from  sample_test;']





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