How to retrieve the title of the x axis for an altair chart?

If I have an altair Chart python object, is there a way for me to retrieve the title of the x axis of this chart? I am writing a function that takes in a chart and I want to check whether there's a title.

There is a couple of ways to achieve this depending on how the chart was configured.

A reliable way is to convert the chart to a dictionary and look for the title.

Lets say you have a chart created like so:

chart = alt.Chart(data).mark_line().encode(
    x=alt.X('x', title='X-Axis Title'),
    y=alt.Y('y', title='Y-Axis Title')
).properties(
    title='Sample Chart'
)

You convert to dictionary and retrieve the x_axis title like this:

def get_x_axis_title_method_dictionary(chart):
    chart_dict = chart.to_dict()
    
    # Try to get title from encoding
    if 'encoding' in chart_dict and 'x' in chart_dict['encoding']:
        if 'title' in chart_dict['encoding']['x']:
            return chart_dict['encoding']['x']['title']
        
        # Check if title is in the axis property
        if 'axis' in chart_dict['encoding']['x'] and 'title' in chart_dict['encoding']['x']['axis']:
            return chart_dict['encoding']['x']['axis']['title']
            
    return None

First you need to check if the encoding key exists, if yes then you check if an x key exists. If they both exist then the x-axis encoding is defined and you can retrieve it as shown above.

Another way is using chart properties.

def get_x_axis_title_method_properties(chart):
    if hasattr(chart, 'encoding') and hasattr(chart.encoding, 'x'):
        # Accessing the internal _kwds dictionary where actual values are stored
        if hasattr(chart.encoding.x, '_kwds') and 'title' in chart.encoding.x._kwds:
            return chart.encoding.x._kwds['title']
        # For axis-defined titles
        if hasattr(chart.encoding.x, 'axis') and hasattr(chart.encoding.x.axis, '_kwds'):
            if 'title' in chart.encoding.x.axis._kwds:
                return chart.encoding.x.axis._kwds['title']
    return None

When you access chart.encoding.x.title, you're not getting the string value directly, but instead a property setter object that manages the title attribute. Therefore, you need to access the internal _kwds dictionary of the property setter objects. This is less reliable as Altair's internal implementation details could change in the future so the dictionary method is preferred.