Default template variables

[Theron Luhn]

I can pass variables into my template by returning them in a dictionary from the view controller. However, if I try to access a variable from the template that I didn't pass, I'll get an error.  Is it possible to have a default value so I don't get an error? Maybe with BeforeRender or something?

- Theron

[Robert Forkel]

If you are using mako, you may want to have a look at
http://docs.makotemplates.org/en/latest/runtime.html#context-variables
and adapt the strict_undefined setting in your config.
regards
robert

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[Theron Luhn]

I'm using Chameleon :\

On Tuesday, May 8, 2012 9:51:00 PM UTC-7, Robert Forkel wrote:

If you are using mako, you may want to have a look at
http://docs.makotemplates.org/en/latest/runtime.html#context-variables
and adapt the strict_undefined setting in your config.
regards
robert

On Wed, May 9, 2012 at 6:27 AM, Theron Luhn <the...@luhn.com> wrote:
> I can pass variables into my template by returning them in a dictionary from
> the view controller. However, if I try to access a variable from the
> template that I didn't pass, I'll get an error.  Is it possible to have a
> default value so I don't get an error? Maybe with BeforeRender or something?
>
> - Theron
>
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[Erik Buttram]

You can use tal:on-error to substitute content in case there's a NameError.  There's a couple other ideas/suggestions on this question on stack overflow:

http://stackoverflow.com/questions/8854179/chameleon-zpt-templates

I've tried using tal:one-error and it seems to work if your only using the variable to fill the content of an element.  Haven't used it for anything more advanced than that though.

[Malthe Borch]

On 9 May 2012 06:27, Theron Luhn <the...@luhn.com> wrote:
> I can pass variables into my template by returning them in a dictionary from
> the view controller. However, if I try to access a variable from the
> template that I didn't pass, I'll get an error.  Is it possible to have a
> default value so I don't get an error?

Yes!

You can use the "|" operator:

<div>
Hello, ${name | "world"}.
</div>

(Note that you can even use it several times, to provide multiple
"fallback" expressions.

\malthe

[Raj]

You can create an 'h' helper object as described here--> http://docs.pylonsproject.org/projects/pyramid_cookbook/en/latest/templates/templates.html#using-a-before-render-event-to-expose-an-h-helper-object

or just have a subscribers.py file with:

@subscriber(BeforeRender)

def template_globals(event):

    request = event['request']  ## this is how you access the request object in this function

    from datetime import datetime

    event.update({'someglobalvar': 'this is my global value',

                                  'thedate': datetime.now})

    return ##no need to return anything

Then you can just do ${thedate()} in any of your templates.

-Raj

[Raj]

In the second example, config.scan() finds your @subscriber(BeforeRender)

[Theron Luhn]

Malthe's solution is the simplest and it works perfectly.  But thank you all for your answers!

- Theron

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[Jonathan Vanasco]

Pylons had the concept of an attribute-safe object ( see below )

I toss it in /lib/helpers and use them throughout my code. I
typically have my core handler stash an instance or two in the request
object. All my template variables look to read off this object.



=======

class AttributeSafeObject(object):
"""object, with lax attribute access ( returns '' when the
attribute does not exist). Based on pylons."""

def __init__(self,**kwargs):
for key in kwargs:
setattr(self,key,kwargs[key])

def __getattr__(self, name):
try:
return object.__getattribute__(self,name)
except AttributeError:
if 0:
log.debug("No attribute called %s found on
AttributeSafeObject object, returning empty string", name)
return ''

[Максим Коринец]

To add to other answers - while using Mako I sometimes implement default rendering like this:

<div>${variable or 'some default value'}</div>

So, if variable is None, some default value is rendered. Don't know if this will work with Chameleon though.

[Malthe Borch]

Yep, it will.

Alternatively, you can use the ternary operator if you strictly want
to guard against ``None``:

${variable if variable is not None else 'some default value'}

\malthe

[Marco Mariani]

On 14 May 2012 09:26, Malthe Borch <mbo...@gmail.com> wrote:

> Alternatively, you can use the ternary operator if you strictly want
> to guard against ``None``:
>
>  ${variable if variable is not None else 'some default value'}

To keep it readable, I have an utility function available to all templates:

> def coalesce(*seq):
> el = None
> for el in seq:
> if el is not None:
> return el
> return el

then it becomes ${coalesce(variable, 'some default value')}

and sometimes this one:

> def coalesce_wrap(wrapper, *seq):
> el = coalesce(*seq)
> if el is not None:
> return wrapper(el)
> else:
> return None