Jay Taylor | programmer notes

Archive for April 2010



URLDecode for Python one-liner

Googling for “python urldecode” led me to this, which contained a solution:

import re

def htc(m):
    return chr(int(m.group(1),16))

def urldecode(url):
    rex = re.compile('%([0-9a-hA-H][0-9a-hA-H])',re.M)
    return rex.sub(htc,url)

However, it is seems a overly complex and confusing when it could instead be equivalently  represented like this:

import re
_ud = re.compile('%([0-9a-hA-H]{2})', re.MULTILINE)
urldecode = lambda x: _ud.sub(lambda m: chr(int(m.group(1), 16)), x)

Surely you agree ;)

*Update Dec 6th, 2011*
Okay, so this came up up today when I searched for “python one-liner urldecode” [yea, I forgot that I wrote this! ^^], and I noticed that this isn’t actually a one-liner! Here is a the version with several statements crammed into one line:

import re,sys;print re.sub(r'%([0-9a-hA-H]{2})',lambda m: chr(int(m.group(1),16)), open(sys.argv[1]).read() if len(sys.argv) > 1 else sys.stdin.read())

And here is my .bash_profile alias that I use to make this conveniently accessible from the command line:

alias urldecode="python -c \"import re,sys;print re.sub(r'%([0-9a-hA-H]{2})',lambda m: chr(int(m.group(1),16)), open(sys.argv[1]).read() if len(sys.argv) > 1 else sys.stdin.read())\""

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Django + Oracle = …

Django + Oracle = one error after another.

It took 3 hours just to get the Oracle DB driver installed and working (ended up linking all the Oracle xxx.so libs into /lib64/xxx.so, and that worked.

Then I created my models:

class Customer(models.Model):
 id = models.IntegerField(primary_key=True)
 name = models.CharField(max_length=100)
 phone_number = models.CharField(max_length=40)
 address = models.CharField(max_length=100)
 city = models.CharField(max_length=50)
 state = models.CharField(max_length=2)
 zipcode = models.CharField(max_length=10)
 date_created = models.DateField(auto_now_add=True)
 financial_info = models.CharField(max_length=255)

 def __unicode__(self):
 return self.name

 class Meta:
 db_table = 'CUSTOMER'
 db_tablespace = 'tables'

When I went into the AdminSite to create a customer, everything seemed to be working well.  I filled out the form, pressed “Save”, and then was greeted with a lovely error page:

DatabaseError at /admin/jjauto/customer/add/
ORA-00904: "CUSTOMER"."ID": invalid identifier

Googling this term + django, I found that there was a ticket which had the same error. At the bottom it said a fix had been integrated with the latest SVN version.

I figured out how to run different versions of Django concurrently so as not to break my other sites running fine with Django 1.1.1.  After all this, I still got the same error when creating a new customer.

At this point I started digging again and discovered the SQL query that is causing the error:


So I took the query and modified it to use lower-case column names:

SELECT * FROM (SELECT ROWNUM AS "_RN", "_SUB".* FROM (SELECT "EMPLOYEE"."id", "EMPLOYEE"."name", "EMPLOYEE"."phone_number", "EMPLOYEE"."address", "EMPLOYEE"."city", "EMPLOYEE"."state", "EMPLOYEE"."zipcode", "EMPLOYEE"."date_created" FROM "EMPLOYEE" WHERE "EMPLOYEE"."id" = 1 ) "_SUB" WHERE ROWNUM <= 21) WHERE "_RN" > 0;

I ran it in SQL Developer and it executed fine, returning no hits.

It is becoming apparent that the problem is Django taking each column (e.g. “id”), and creating the table with the column name (e.g. “id”, lower-cased), but then when it runs this query, the column names become upper-case (i.e. “ID”).  Ok, that is dumb and should probably not be happening, but I’ll try and work with what I’ve got here.  I found the option to override the column names, and used a little vimfu to make it painless:

%s/^\(\s\+\)\([^ ]\+\)\( = .*\))$/\1\2\3, db_column='\U\2')/ge | %s/(, /(/ge


class Customer(models.Model):
 id = models.IntegerField(primary_key=True, db_column='ID')
 name = models.CharField(max_length=100, db_column='NAME')
 phone_number = models.CharField(max_length=40, db_column='PHONE_NUMBER')
 address = models.CharField(max_length=100, db_column='ADDRESS')
 city = models.CharField(max_length=50, db_column='CITY')
 state = models.CharField(max_length=2, db_column='STATE')
 zipcode = models.CharField(max_length=10, db_column='ZIPCODE')
 date_created = models.DateField(auto_now_add=True, db_column='DATE_CREATED')
 financial_info = models.CharField(max_length=255, db_column='FINANCIAL_INFO')

 def __unicode__(self):
 return self.name

 class Meta:
 db_table = 'CUSTOMER'

Finally, the inserts work :) What a PITA…

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