I can not understand this behavior at all. I asked a question yesterday or the day before thinking it was something with bottle.py, but after trying all kinds of possible solutions, even converting my app over to flask, I have pinpointed the behavior to a single, very simple, class, but I have NO idea why this is happening. It's confusing the hell out of me, but I would really like to understand this if anyone can please shed some light on it.
Ok, so first I have a class called Page which simplifies setting up templates a bit, this is the offending class:
class Page:
"""The page object constructs the webpage and holds associated variables and templates"""
def __init__(self, template=None, name = '', title='',template_vars={}, stylesheets=[], javascript=[]):
# Accepts template with or without .html extension, but must be added for lookup
self.stylesheet_dir = '/css'
self.javascript_dir = '/js'
self.template = template
self.template_vars = {}
self.name = name
self.title = title
self.stylesheets = stylesheets
self.javascript = javascript
self.template_vars['debug'] = _Config.debug
self.template_vars['title'] = self.title
self.template_vars['stylesheets'] = self.stylesheets
self.template_vars['javascript'] = self.javascript
def render(self):
"""Should be called after the page has been constructed to render the template"""
if not self.template.endswith(_Config.template_extension):
self.template += '.' + _Config.template_extension
if not self.title:
if self.name:
self.title = _Config.website + _Config.title_delimiter + self.name
else:
# If title not given use template name
self.title = _Config.website + _Config.title_delimiter + self.template.rstrip('.html')
try:
template = env.get_template(self.template)
except AttributeError:
raise (AttributeError, 'template not set')
rendered_page = template.render(self.template_vars)
return rendered_page
def add_stylesheet(self, name, directory=None):
# Sanitize name
if not name.endswith('.css'):
name += '.css'
if name.startswith('/'):
name = name.lstrip('/')
if not directory:
directory = self.stylesheet_dir
self.template_vars['stylesheets'].append(directory + '/' + name)
def add_javascript(self, name, directory=None):
# Sanitize name
if not name.endswith('.js'):
name += '.js'
if name.startswith('/'):
name = name.lstrip('/')
if not directory:
directory = self.javascript_dir
self.template_vars['javascript'].append(directory + '/' + name)
And here is an example of a route that the problem is exhibited:
@route('/create_account', method=['GET','POST'])
def create_account():
dbsession = db.Session()
page = Page('create account')
page.add_javascript('create_account.js')
if request.method == 'GET':
page.template = 'create_account'
page.template_vars['status'] = None
document = page.render()
dbsession.close()
return document
elif request.method == 'POST':
# Omitted
The problem lies with the method Page.add_javascript(). The next time I go to the /create_account page it is not creating a new Page object and instead reusing the old one. I know this because if I go to the page twice I will have two entires for the create_account.js in my returned html document(the template simply runs a for loop and creates a tag for any js files passed in that list). If I go 3 times it'll be listed 3 times, 40, 40 and so on. Now however if I simply change it to use the initializer and not the add_javascript method the problem goes away.
@route('/create_account', method=['GET','POST'])
def create_account():
dbsession = db.Session()
page = Page('create account', javascript=['create_account.js'])
if request.method == 'GET':
page.template = 'create_account'
page.template_vars['status'] = None
document = page.render()
dbsession.close()
return document
elif request.method == 'POST':
However I suspect something is still wrong and just for my own sanity I need to understand what the hell is going on here. What is possibly happeneing behind the scenes where the add_javascript method would be called twice on the same page object? The method is called immediately after creating a new instance of the page object, where is it possibly getting the old contents of template_vars from?
The problem is that you use mutable defaults for your Page.__init__ function. See http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments.
So you do get a new Page instance on each request, but the lists/dictionaries that hold your javascript etc are re-used.
Replace list/dict default argument values with None, check for None in __init__.