Blog snippets: shrtn

convert.py

def convert_to_code(id, alphabet=ALPHABET):
    """Converts a decimal id number into a shortened URL code. Use the id of the
    row in the database with the entered long URL."""
    if id <= 0: #invalid codes (autoincrement is always 1 or higher)
        return alphabet[0]
    
    base = len(alphabet) #base to convert to (56 for our standard alphabet)
    chars = []
    while id:
        chars.append(alphabet[id % base])
        id //= base
    chars.reverse() #moved right to left, so reverse order
    return ''.join(chars) #convert stored characters to single string

database_search.py

def search_url(url, table, conn):
    """Attempts to find a row in the table in the database conn with the given
    url. Returns its id value if it is present, returns False otherwise."""
    query = 'select * from %s where original="%s"' % (table, url)
    result = conn.execute(query).fetchall()
    if not result: #url not in our database, return False
        return False
    else:
        return result[0][0] #return the id of the url
    
def search_id(id, table, conn):
    """Attempts to find a row in the table in the database conn with the given
    id. Returns its url value if it is present, returns False otherwise."""
    query = 'select * from %s where id=%d' % (table, id)
    result = conn.execute(query).fetchall()
    if not result: #id not in our database, return False
        return False
    else:
        return str(result[0][1]) #return the url of the id

database_setup.py

def setup_sql(location):
    """Establishes a connection to the sqlite database at location and returns 
    the database connection object."""
    try:
        conn = sql.connect(location)
        return conn
    except sql.OperationalError:
        print "Error: could not open database file at '%s'" % location
        return None

lengthen.py

def lengthen_url(url, conn):
    """Takes in one of our shortened URLs and returns the correct long url."""
    #isolate code from shortened url
    if not is_valid_short(url): #url was not constructed properly
        return "%s404" % OURDOMAIN
    code = url[14:] #just the code, ie. h7K9g0
    
    id = resolve_to_id(code) #convert shortened code to id
    long = db.search_id(id, db.MYTABLE, conn)
    if not long: #id was not found in database
        return "%s404" % OURDOMAIN #issue 404
    return long #url to perform 301 re-direct on

resolve.py

def resolve_to_id(code, alphabet=ALPHABET):
    """Converts the shortened URL code back to an id number in decimal form. Use
    the id to query the database and lookup the long URL."""
    base = len(alphabet)
    size = len(code)
    id = 0
    for i in range(0, size): #convert from higher base back to decimal
        id += alphabet.index(code[i]) * (base ** (size-i-1))
    return id

urls.py

def insert_url(url, table, conn):
    """Inserts the url into the table in the database conn and returns the id
    of the row which was created by the insert."""
    query = 'insert into %s values(NULL, "%s")' % (table, url)
    c = conn.execute(query)
    return c.lastrowid #autoincremented id of the just inserted row

def shorten_url(url, conn):
    """Takes in a standard url and returns a shortened version."""
    url = standardize_url(url)
    if url is None: #tried to shorten invalid url
        return None
    
    #get the id for this url (whether new or otherwise)
    id = db.search_url(url, db.MYTABLE, conn)
    if not id: #url not yet inserted into database
        id = db.insert_url(url, db.MYTABLE, conn) #insert and get its id
    
    code = convert_to_code(id)
    return "%s%s" % (OURDOMAIN, code)