How to catch index error

[Maurice Waka]

I have a code that works OK except when there is no data in the database.

Here is the code, using MongoDB.

model code:

db.define_table('sleep',

                Field('awake','double',default=0),

                Field('light_sleep','double',default=0),

                Field('deep_sleep','double',default=0),

                Field('author', 'reference auth_user', default=auth.user_id, readable=False, writable=False),

                common_filter = lambda query: db.sleep.author == auth.user_id)

def sleep_chart():

    response.files.append(URL('e_default','static/js/pygal-tooltips.min.js'))

    response.headers['Content-Type']='image/svg+xml'

    custom_style = Style(

        background='transparent',

        plot_background='transparent',

        foreground='#53E89B',

        foreground_strong='#53A0E8',

        foreground_subtle='#630C0D',

        opacity='.6',

        opacity_hover='.9',

        transition='400ms ease-in',

        colors=('#E853A0', '#E8537A', '#E95355', '#E87653', '#E89B53')

        )

    data = db(db.sleep).select()

    gauge = pygal.SolidGauge(inner_radius=0.70)

    percent_formatter = lambda x: '{:.10g}Hrs'.format(x)

    gauge.value_formatter = percent_formatter

    gauge.add('Awake', [{'value':[i.awake for i in data][-1], 'max_value': 24}])

    gauge.add('Light Sleep', [{'value':[i.light_sleep for i in data][-1], 'max_value': 24}])

    gauge.add('Deep Sleep', [{'value':[i.deep_sleep for i in data][-1], 'max_value': 24}])

    return gauge.render()

def mySleep():

    chart= URL('default', 'sleep_chart')

    form = SQLFORM(db.sleep, submit_button=T('Submit')).process()

    return dict(chart = chart,form=form)

Here is the problem:

When a new user registers into the system, by default, there is no data recorded in the database, so I get the error(see attached) below.

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 Traceback (most recent call last):
 File "/home/mau/web2py/gluon/restricted.py", line 219, in restricted
 exec(ccode, environment)
 File "/home/mau/web2py/applications/Hesty/controllers/e_default.py", line 708, in <module>
 File "/home/mau/web2py/gluon/globals.py", line 421, in <lambda>
 self._caller = lambda f: f()
 File "/home/mau/web2py/gluon/tools.py", line 3868, in f
 return action(*a, **b)
 File "/home/mau/web2py/applications/Hesty/controllers/e_default.py", line 649, in sleep_chart
 gauge.add('Awake', [{'value':[i.awake for i in data][-1], 'max_value': 24}])
IndexError: list index out of range

Expectation:I want to have a default figure in the database. I have tried having "default=0" but the int only appears in the form text area. So the error persists.

Is there a way to have a default figure in the database or a way to catch this errors and let the new user to input int figure?

[isi_jca]

def sleep_chart():

    response.files.append(URL('e_default','static/js/pygal-tooltips.min.js'))

    response.headers['Content-Type']='image/svg+xml'

    custom_style = Style(

        background='transparent',

        plot_background='transparent',

        foreground='#53E89B',

        foreground_strong='#53A0E8',

        foreground_subtle='#630C0D',

        opacity='.6',

        opacity_hover='.9',

        transition='400ms ease-in',

        colors=('#E853A0', '#E8537A', '#E95355', '#E87653', '#E89B53')

        )

    data = db(db.sleep).select()

    gauge = pygal.SolidGauge(inner_radius=0.70)

    percent_formatter = lambda x: '{:.10g}Hrs'.format(x)

    gauge.value_formatter = percent_formatter

    # check if the select retrieve data

    if data:

         gauge.add('Awake', [{'value':[i.awake for i in data][-1], 'max_value': 24}])

         gauge.add('Light Sleep', [{'value':[i.light_sleep for i in data][-1], 'max_value': 24}])

         gauge.add('Deep Sleep', [{'value':[i.deep_sleep for i in data][-1], 'max_value': 24}])

    else:

         gauge.add('Awake', [{'value':0, 'max_value': 24}])

         gauge.add('Light Sleep', [{'value':0, 'max_value': 24}])

         gauge.add('Deep Sleep', [{'value':0, 'max_value': 24}])

    return gauge.render()

[Dave S]

On Tuesday, March 19, 2019 at 11:57:35 AM UTC-7, Maurice Waka wrote:

I have a code that works OK except when there is no data in the database.

[...]

    gauge.add('Awake', [{'value':[i.awake for i in data][-1], 'max_value': 24}])

    gauge.add('Light Sleep', [{'value':[i.light_sleep for i in data][-1], 'max_value': 24}])

    gauge.add('Deep Sleep', [{'value':[i.deep_sleep for i in data][-1], 'max_value': 24}])

    return gauge.render()

[...]


 File "/home/mau/web2py/applications/Hesty/controllers/e_default.py", line 649, in sleep_chart

 gauge.add('Awake', [{'value':[i.awake for i in data][-1], 'max_value': 24}])
IndexError: list index out of range

Expectation:I want to have a default figure in the database. I have tried having "default=0" but the int only appears in the form text area. So the error persists.

Is there a way to have a default figure in the database or a way to catch this errors and let the new user to input int figure?

The simplistic way is to wrap the lines I left in the quoted material:

if len(data):

    gauge.add('Awake', [{'value':[i.awake for i in data][-1], 'max_value': 24}])
    gauge.add('Light Sleep', [{'value':[i.light_sleep for i in data][-1], 'max_value': 24}])
    gauge.add('Deep Sleep', [{'value':[i.deep_sleep for i in data][-1], 'max_value': 24}])

else:
    gauge.add('Unknown', [{'value':[0], 'max_value': 24}])

A better person than I might put the if into the comprehension, but I tend not to get that right.

/dps

[Leonel Câmara]

Notice that, it seems you are using [-1] because want to get the last record where the user was awake/light sleep/sleep, however you don't use an order by, so depending on the strategy the database decides to use, there's no guarantee that it will be the last. This is also inefficient because you only want the last record and you're getting all the records and they could be hundreds in the future.

Couldn't you just do:

    last_sleep = db(db.sleep.id > 0).select(orderby=~db.sleep.id, limitby=(0,1)).first()
    gauge.add('Awake', [{'value':last_sleep.awake if last_sleep else 0, 'max_value': 24}])
    gauge.add('Light Sleep', [{'value':last_sleep.light_sleep if last_sleep else 0, 'max_value': 24}])
    gauge.add('Deep Sleep', [{'value':last_sleep.deep_sleep if last_sleep else 0, 'max_value': 24}])

[Maurice Waka]

This works well Boss!!

Thanks a lot and God Bless!

Regards

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[Dave S]

On Tuesday, March 19, 2019 at 5:45:42 PM UTC-7, Leonel Câmara wrote:

Notice that, it seems you are using [-1] because

I thought he was doing that to test our ability to count brackets, braces, and parens.  (GG's default font, as used on my screen, makes them very close in appearance; using the code wrapper helps by monospacing.)
 

and there you see an example of what I have a hard time doing right ... conditionals in comprehensions.

/dps