# <py-script> The `` element lets you execute multi-line Python scripts both inline and via a src attribute. ## Attributes | attribute | type | default | description | |-----------|--------|---------|------------------------------| | **src** | url | | You don't need to add long python code in py-script, you can provide url of the python source file in the py-script tag with the `src` attribute. When a Python file is referred with the `src` attribute it is executed, and then added to the namespace where it was referred. | | **output**| string | | The id of a DOM element to route `sys.stdout` and `stderr` to, in addition to sending it to the ``| | **stderr**| string | | The id of a DOM element to route just `sys.stderr` to, in addition to sending it to the ``| ### output If the `output` attribute is provided, any output to [sys.stdout](https://docs.python.org/3/library/sys.html#sys.stdout) or [sys.stderr](https://docs.python.org/3/library/sys.html#sys.stderr) is written to the DOM element with the ID matching the attribute. If no DOM element is found with a matching ID, a warning is shown. The msg is output to the `innerHTML` of the HTML Element, with newlines (`\n'`) converted to breaks (``). This output is in addition to the output being written to the developer console and the `` if it is being used. ### stderr If the `stderr` attribute is provided, any output to [sys.stderr](https://docs.python.org/3/library/sys.html#sys.stderr) is written to the DOM element with the ID matching the attribute. If no DOM element is found with a matching ID, a warning is shown. The msg is output to the `innerHTML` of the HTML Element, with newlines (`\n'`) converted to breaks (``). This output is in addition to the output being written to the developer console and the `` if it is being used. ## Examples ### Inline `` element Let's execute this multi-line Python script to compute π and print it back onto the page ```html print("Let's compute π:") def compute_pi(n): pi = 2 for i in range(1,n): pi *= 4 * i ** 2 / (4 * i ** 2 - 1) return pi pi = compute_pi(100000) s = f"π is approximately {pi:.3f}" print(s) ``` ### Using `` element with `src` attribute we can also move our python code to its own file and reference it via the `src` attribute. ```python # compute_pi.py print("Let's compute π:") def compute_pi(n): pi = 2 for i in range(1,n): pi *= 4 * i ** 2 / (4 * i ** 2 - 1) return pi pi = compute_pi(100000) s = f"π is approximately {pi:.3f}" print(s) ``` Since both compute_pi.py and index.html are in the same directory, we can reference the python file with a relative path. ```html ``` ### Writing into labeled elements In the example above, we had a single `` tag printing one or more lines onto the page in order. Within the ``, you can use the `Element` class to create a python object for interacting with page elements. Objects created from the `Element` class provide the `.write()` method which enables you to send strings into the page elements referenced by those objects. For example, we'll add some style elements and provide placeholders for the `` tag to write to. ```html Today is

import datetime as dt Element('today').write(dt.date.today().strftime('%A %B %d, %Y')) def compute_pi(n): pi = 2 for i in range(1,n): pi *= 4 * i ** 2 / (4 * i ** 2 - 1) return pi pi = compute_pi(100000) Element('pi').write(f'π is approximately {pi:.3f}') ```