blocks|key|4713409|text|使用none+test+(不要与Python的None+object混淆！)：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4713410|{%25+if+p+is+not+none+%25}+++
++++{{+p.User['first_name']+}}
{%25+else+%25}
++++NONE
{%25+endif+%25}|code-block|syntax|javascript|4713411|或者：|4713412|{{+p.User['first_name']+if+p+is+not+none+else+'NONE'+}}|4713413|或者，如果您需要一个空字符串：|4713414|{{+p.User['first_name']+if+p+is+not+none+}}|4713415|entityMap|0|LINK|mutability|MUTABLE|url|https://jinja.palletsprojects.com/en/2.11.x/templates/#none|1|https://docs.python.org/3/library/constants.html^0|2|4|N|4|2|9|0|N|B|1|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@$9|17|A|18|1|19]|$9|1A|A|1B|1|1C]]|E|$]]|$1|F|3|G|5|H|7|1D|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1E|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1F|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1G|8|@]|D|@]|E|$]]|$1|Q|3|R|5|H|7|1H|8|@]|D|@]|E|$I|J]]|$1|S|3|-4|5|6|7|1I|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]|10|$5|V|W|X|E|$Y|11]]]]

Use the <a href="https://jinja.palletsprojects.com/en/2.11.x/templates/#none" rel="noreferrer"><code>none</code> test</a> (not to be confused with Python's <a href="https://docs.python.org/3/library/constants.html" rel="noreferrer"><code>None</code> object</a>!):
<pre><code>{% if p is not none %} 
 {{ p.User['first_name'] }}
{% else %}
 NONE
{% endif %}
</code></pre>
or:
<pre><code>{{ p.User['first_name'] if p is not none else 'NONE' }}
</code></pre>
or if you need an empty string:
<pre><code>{{ p.User['first_name'] if p is not none }}
</code></pre>

blocks|key|4713505|text|{{p.User['first_name']+or+'My+default+string'}}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|4713506|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>{{p.User['first_name'] or 'My default string'}}
</code></pre>

blocks|key|4713564|text|根据docs的说法，你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4713565|{{+p%7Cd('',+true)+}}|code-block|syntax|javascript|4713566|导致在布尔上下文中将None强制转换为False。|style|CODE|4713567|entityMap|0|LINK|mutability|MUTABLE|url|https://jinja.palletsprojects.com/en/3.0.x/templates/#jinja-filters.default^0|2|4|0|0|0|A|4|J|5|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]|$A|12|B|13|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

According to <a href="https://jinja.palletsprojects.com/en/3.0.x/templates/#jinja-filters.default" rel="nofollow noreferrer">docs</a> you can just do:
<pre><code>{{ p|d('', true) }}
</code></pre>
Cause <code>None</code> casts to <code>False</code> in a boolean context.

blocks|key|207580|text|除了其他答案，如果变量不是这样的，你可以写一些其他的东西：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|207581|{{+variable+or+''+}}|code-block|syntax|javascript|207582|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

As addition to other answers, one can write something else if variable is None like this:

<pre><code>{{ variable or '' }}
</code></pre>

blocks|key|4713499|text|遵循this+doc，你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4713500|{{+p.User['first_name']%7Cdefault('NONE')+}}|code-block|syntax|javascript|4713501|entityMap|0|LINK|mutability|MUTABLE|url|http://jinja.pocoo.org/docs/templates/#builtin-filters^0|2|8|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Following <a href="http://jinja.pocoo.org/docs/templates/#builtin-filters" rel="noreferrer">this doc</a> you can do this that way:

<pre><code>{{ p.User['first_name']|default('NONE') }}
</code></pre>

blocks|key|4713651|text|为了避免在"p“或"p.User”为None时抛出异常，您可以使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4713652|{{+(p+and+p.User+and+p.User['first_name'])+or+"default_value"+}}|code-block|syntax|javascript|4713653|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

To avoid throw a exception while "p" or "p.User" is None, you can use:

<pre><code>{{ (p and p.User and p.User['first_name']) or "default_value" }}
</code></pre>

blocks|key|207760|text|使用ChainableUndefined，您可以做到这一点。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|207761|>>>+import+jinja2
>>>+env+=+jinja2.Environment(undefined=jinja2.ChainableUndefined)
>>>+env.from_string("{{+foo.bar['baz']+%7C+default('val')+}}").render()
'val'|code-block|syntax|javascript|207762|source|207763|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/pallets/jinja/pull/997^0|2|I|0|0|0|6|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|M|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

With <code>ChainableUndefined</code>, you can do that.
<pre class="lang-py prettyprint-override"><code>&gt;&gt;&gt; import jinja2
&gt;&gt;&gt; env = jinja2.Environment(undefined=jinja2.ChainableUndefined)
&gt;&gt;&gt; env.from_string(&quot;{{ foo.bar['baz'] | default('val') }}&quot;).render()
'val'
</code></pre>
<a href="https://github.com/pallets/jinja/pull/997" rel="nofollow noreferrer">source</a>

blocks|key|207688|text|作为另一种解决方案(类似于之前的一些解决方案)：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|207689|{{+(+p+is+defined+and+p.User+is+defined+and+p.User['first_name']+)+%7Cdefault("NONE",+True)+}}|code-block|syntax|javascript|207690|注意，最后一个变量(p.User‘’first_name‘)后面没有if+defined测试。|offset|length|style|CODE|207691|entityMap^0|0|0|Y|A|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

As another solution (kind of similar to some previous ones):

<pre><code>{{ ( p is defined and p.User is defined and p.User['first_name'] ) |default("NONE", True) }}
</code></pre>

Note the last variable (p.User['first_name']) does not have the <code>if defined</code> test after it.

blocks|key|207794|text|如果您想设置自己的缺省值而不是无，那么只需执行以下操作|type|unstyled|depth|inlineStyleRanges|entityRanges|data|207795|{{your_var%7Cdefault:'default+name'}}|offset|length|style|CODE|207796|entityMap^0|0|0|Z|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

if you want to set your own default value instead of None than simply do this
<code>{{your_var|default:'default name'}}</code>

blocks|key|4713685|text|我通常定义一个nvl函数，并将其放在globals和filters中。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|4713686|def+nvl(*args):
++++for+item+in+args:
++++++++if+item+is+not+None:
++++++++++++return+item
++++return+None

app.jinja_env.globals['nvl']+=+nvl
app.jinja_env.filters['nvl']+=+nvl|code-block|syntax|javascript|4713687|模板中的用法：|4713688|Welcome+{{+nvl(person.nick,+person.name,+'Anonymous')+}}

//+or+

Welcome+{{+person.nick+%7C+nvl(person.name,+'Anonymous')+}}|4713689|entityMap^0|7|3|I|7|Q|7|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]|$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|Y|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|P|$]]

I usually define an <code>nvl</code> function, and put it in <code>globals</code> and <code>filters</code>.

<pre><code>def nvl(*args):
 for item in args:
 if item is not None:
 return item
 return None

app.jinja_env.globals['nvl'] = nvl
app.jinja_env.filters['nvl'] = nvl
</code></pre>

Usage in a template:

<pre><code>&lt;span&gt;Welcome {{ nvl(person.nick, person.name, 'Anonymous') }}&lt;span&gt;

// or 

&lt;span&gt;Welcome {{ person.nick | nvl(person.name, 'Anonymous') }}&lt;span&gt;
</code></pre>

blocks|key|207722|text|从Ansible+2.8开始，你可以只使用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|207723|{{+p.User['first_name']+}}|code-block|syntax|javascript|207724|请参阅https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.8.html#jinja-undefined-values|offset|length|207725|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.8.html#jinja-undefined-values^0|0|0|3|2S|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

As of Ansible 2.8, you can just use:

<pre><code>{{ p.User['first_name'] }}
</code></pre>

See <a href="https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.8.html#jinja-undefined-values" rel="nofollow noreferrer">https://docs.ansible.com/ansible/latest/porting_guides/porting_guide_2.8.html#jinja-undefined-values</a>

blocks|key|4713768|text|您可以简单地将"default+none“添加到您的变量中，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4713769|{{+your_var+%7C+default('NONE',+boolean=true)+}}|code-block|syntax|javascript|4713770|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can simply add &quot;default none&quot; to your variable as the form below mentioned:
<pre><code>{{ your_var | default('NONE', boolean=true) }}
</code></pre>

How to make a variable in jijna2 default to "" if object is None instead of doing something like this?

<pre><code> {% if p %} 
 {{ p.User['first_name']}}
 {% else %}
 NONE
 {%endif %}
</code></pre>

So if object p is None I want to default the values of p (first_name and last_name) to "".
Basically 

<pre><code>nvl(p.User[first_name'], "")
</code></pre>

Error receiving:

<pre><code>Error: jinja2.exceptions.UndefinedError
 UndefinedError: 'None' has no attribute 'User'
</code></pre>

Jinja2 template variable if None Object set a default value

Python

如果object为None，如何使jijna2中的变量缺省为"“，而不是这样做？      {% if p %}           {{ p.User['first_name']}}      {% else %}        NONE      {%endif %}因此，如果对象p为None，我希望将p (first_name和last_name)的值默认为"“。基本上nvl(p.User[

问如果无对象设置默认值，则为Jinja2模板变量
EN

回答 12

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如果无对象设置默认值，则为Jinja2模板变量EN

回答 12

Stack Overflow用户

Stack Overflow用户

Stack Overflow用户

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如果无对象设置默认值，则为Jinja2模板变量
EN