Template filters in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a template filter in Flask?

A template filter in Flask is a function that modifies or formats data before displaying it in a template. It helps change how data looks without changing the data itself.

beginner

How do you apply a built-in filter in a Flask template?

You apply a filter by using the pipe symbol (|) after a variable in the template. For example, {{ name|upper }} changes the text in 'name' to uppercase.

intermediate

How can you create a custom template filter in Flask?

You create a custom filter by defining a Python function and then registering it with Flask using the @app.template_filter decorator or app.add_template_filter().

intermediate

What is the purpose of using template filters instead of modifying data in the view?

Template filters keep the view code clean and separate data formatting from logic. This makes templates easier to read and maintain.

beginner

Example: What does {{ 3.14159|round(2) }} output in a Flask template?

It outputs 3.14 by rounding the number 3.14159 to 2 decimal places using the built-in 'round' filter.

Which symbol is used to apply a filter to a variable in a Flask template?

A |

B &

C #

D %

The pipe symbol (|) is used to apply filters in Flask templates, like {{ variable|filter }}.

How do you register a custom filter in Flask?

A Using @app.template_filter decorator

B Using @app.route decorator

C Using @app.before_request decorator

D Using @app.errorhandler decorator

Custom filters are registered with @app.template_filter or app.add_template_filter().

What does the built-in 'upper' filter do in Flask templates?

A Converts text to lowercase

B Reverses the text

C Converts text to uppercase

D Removes spaces from text

The 'upper' filter changes all letters in a string to uppercase.

Why use template filters instead of formatting data in the Flask view?

A Filters slow down the app

B Filters change the original data permanently

C Filters are harder to maintain

D Filters keep templates and views separate and clean

Filters help keep formatting in templates, making views simpler and code cleaner.

Which of these is NOT a built-in Flask template filter?

A capitalize

B pluralize

C lower

D round

'pluralize' is not a built-in filter in Flask; you would need to create a custom filter for that.

Explain how to create and use a custom template filter in Flask.

Think about how you connect Python code to templates.

Describe why template filters are useful in Flask templates.

Consider the difference between data and how it looks.