TypeError: Parser must be a string or character stream, not datetime

Question

I'm trying to have a webpage show all of the upcoming shows listed in a database, along with a bunch of info about each show that's stored in venue and artist tables respectively. I query the Show table, and then for each row in that result I link the Artist and Venue tables. Because the error has something to do with datetime, I'm assuming the error is something to do with either if show.start_time > current_time: or "start_time": show.start_time but the error doesn't pin down where it is. I tried converting both current_time and show.start_time to a string just to see if that worked, but no luck. What am I doing wrong?

@app.route('/shows')
def shows():

  current_time = datetime.now()

  data = []

  allshows = Show.query.all()

  for show in allshows:
    artist = Artist.query.get(show.artist_id)
    venue = Venue.query.get(show.venue_id)

    if show.start_time > current_time:
      data.append({
        "venue_id": show.venue_id,
        "venue_name": venue.name,
        "artist_id": show.artist_id,
        "artist_name": artist.name,
        "artist_image_link": artist.image_link,
        "start_time": show.start_time
      })
 
  return render_template('pages/shows.html', shows=data)

If it helps, here are the models associated with it:

class Venue(db.Model):
    __tablename__ = 'venues'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    city = db.Column(db.String(120))
    state = db.Column(db.String(120))
    address = db.Column(db.String(120))
    phone = db.Column(db.String(120))
    image_link = db.Column(db.String(500))
    facebook_link = db.Column(db.String(120))
    genres = db.Column(db.ARRAY(db.String))
    image_link = db.Column(db.String(500))
    facebook_link = db.Column(db.String(120))
    website = db.Column(db.String(300))
    seeking_talent = db.Column(db.Boolean)
    seeking_description = db.Column(db.String(120))
    shows = db.relationship('Show', backref='venue', lazy=True)

class Artist(db.Model):
    __tablename__ = 'artists'

    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String)
    city = db.Column(db.String(120))
    state = db.Column(db.String(120))
    phone = db.Column(db.String(120))
    genres = db.Column(db.String(120))
    image_link = db.Column(db.String(500))
    facebook_link = db.Column(db.String(120))
    website = db.Column(db.String(300))
    seeking_shows = db.Column(db.Boolean)
    seeking_description = db.Column(db.String(120))
    shows = db.relationship('Show', backref='artist', lazy=True)        

class Show(db.Model):
    __tablename__ = 'shows'

    id = db.Column(db.Integer, primary_key=True)
    artist_id = db.Column(db.Integer, db.ForeignKey('artists.id'), nullable = False)
    venue_id = db.Column(db.Integer, db.ForeignKey('venues.id'), nullable = False)
    start_time = db.Column(db.DateTime, nullable = False)

    def __repr__(self):
        return '<Show {} {}>'.format(self.artist_id, self.venue_id)

Edit: Including full traceback.

Traceback (most recent call last):
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 2464, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 2450, in wsgi_app
    response = self.handle_exception(e)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 1867, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 2447, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 1952, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 1821, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/_compat.py", line 39, in reraise
    raise value
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/app.py", line 547, in shows
    return render_template('pages/shows.html', shows=data)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/templating.py", line 137, in render_template
    return _render(
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/flask/templating.py", line 120, in _render
    rv = template.render(context)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/jinja2/environment.py", line 1090, in render
    self.environment.handle_exception()
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/jinja2/environment.py", line 832, in handle_exception
    reraise(*rewrite_traceback_stack(source=source))
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/jinja2/_compat.py", line 28, in reraise
    raise value.with_traceback(tb)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/templates/pages/shows.html", line 1, in top-level template code
    {% extends 'layouts/main.html' %}
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/templates/layouts/main.html", line 103, in top-level template code
    {% block content %}{% endblock %}
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/templates/pages/shows.html", line 9, in block "content"
    <h4>{{ show.start_time|datetime('full') }}</h4>
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/app.py", line 101, in format_datetime
    date = dateutil.parser.parse(value)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/dateutil/parser.py", line 1168, in parse
    return DEFAULTPARSER.parse(timestr, **kwargs)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/dateutil/parser.py", line 556, in parse
    res, skipped_tokens = self._parse(timestr, **kwargs)
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/dateutil/parser.py", line 675, in _parse
    l = _timelex.split(timestr)         # Splits the timestr into tokens
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/dateutil/parser.py", line 192, in split
    return list(cls(s))
  File "/Users/ZEMEL/Dropbox (Personal)/Code/fyyurr/env/lib/python3.8/site-packages/dateutil/parser.py", line 60, in __init__
    raise TypeError('Parser must be a string or character stream, not '
TypeError: Parser must be a string or character stream, not datetime

Edit 2: def that formats datetime:

def format_datetime(value, format='medium'):
  date = dateutil.parser.parse(value)
  if format == 'full':
      format="EEEE MMMM, d, y 'at' h:mma"
  elif format == 'medium':
      format="EE MM, dd, y h:mma"
  return babel.dates.format_datetime(date, format)

app.jinja_env.filters['datetime'] = format_datetime

Please include the entire traceback. As an aside, those many-to-one relationships are good candidates for (joined) eager loading, so you would not have to fetch the artists and venues one by one. I think I remember you attempting to do just that, did it not work out? — Ilja Everilä
– Ilja Everilä, Commented Aug 5, 2020 at 16:50
@IljaEverilä Traceback added. I honestly don't recall, this has been the most frustrating project I've done since starting to learn programming, and with everything else going on in life/the world my head hasn't been completely clear. I'm sure there's more efficient way to do this, but at this point I just need to get this done, I'm already behind schedule for the course I'm in and still have a few things left to do in this before it's done. — Brandon Zemel
– Brandon Zemel, Commented Aug 5, 2020 at 17:04
The error stems from your shows.html template, where it has <h4>{{ show.start_time|datetime('full') }}</h4>. show.start_time is a datetime, which apparently the datetime('full') filter or so does not like, because it seems to be trying to parse the value as if it were a string. — Ilja Everilä
– Ilja Everilä, Commented Aug 5, 2020 at 17:22
So what would be the fix for this? Is there one without changing the HTML? — Brandon Zemel
– Brandon Zemel, Commented Aug 5, 2020 at 17:24
Have you defined the datetime() filter yourself, or is it provided by the template library or the framework? A somewhat ugly solution would be to format show.start_time as a string before passing to the template, but that's band-aid, and you would have to know what format the parser is happy with (ISO 8601 is a good guess). — Ilja Everilä
– Ilja Everilä, Commented Aug 5, 2020 at 17:27

Ilja Everilä · Accepted Answer · 2020-08-07 05:35:33Z

14

From the traceback it can be seen that the exception is raised during rendering of the template. The date formatting filter in

<h4>{{ show.start_time|datetime('full') }}</h4>

seems to expect string values only, and attempts to parse them to a datetime. On the other hand your models use a proper timestamp type, so the attribute show.start_time is already a datetime instance. One way to fix this mismatch is to alter the formatting filter to accept datetime values as well:

def format_datetime(value, format='medium'):
    # instead of just date = dateutil.parser.parse(value)
    if isinstance(value, str):
        date = dateutil.parser.parse(value)
    else:
        date = value
    ...

answered Aug 7, 2020 at 5:35

Ilja Everilä

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