Javascript error when plotting a column with special characters

The following code throws an error (tested with Altair 2.0.1):

import pandas
import altair
df = pandas.DataFrame({"A column name with 'quotes'" : [1, 2, 3, 4], "A column name without quotes" : [5, 6, 7, 8]})
altair.Chart(df).mark_bar().encode(
    altair.X(df.columns[0], bin=True),
    y='count()',
)

It fails with the error:

Javascript Error: Access path missing closing bracket: A column name with 'quotes'. This usually means there's a typo in your chart specification. See the JavaScript console for the full traceback.

This does not happen when using a column name without quotes (e.g., if I use df.columns[1] instead of df.columns[0]). If I put only one quote instead of two, the error is different:

Javascript Error: Access path missing closing quote: A column name with 'quotes. This usually means there's a typo in your chart specification. See the JavaScript console for the full traceback.

[jakevdp]

Because the escaped version of the field name does not match the pandas column name, Altair cannot infer the type of the column – so you’ll have to specify the type explicitly (just as you do when passing data by URL rather than by dataframe):

iris.columns = ['a', 'b[]', 'c.0', 'd', 'e']
alt.Chart(iris).mark_point().encode(
    x='a',
    y='c\\.0:Q'
)

[jakevdp]

I don’t think Altair should automatically escape quotes: the reason they need to be escaped is that they have special meaning within field strings when not escaped, and I would not want Altair to prevent that use.

I think it would be worth raising an appropriate warning when single quotes, double quotes, square brackets, dots, or back-slashes are used.