Name error: name x is not defined

when i try to implement the pca from your site i get the following. please suggest me what am doing wrong.

NameError Traceback (most recent call last)
in ()
11 for col in range(4):
12 for key in colors:
ā€”> 13 traces.append(Histogram(x=X[y==key, col],
14 opacity=0.75,
15 xaxis=ā€˜x%sā€™ %(col+1),

NameError: name ā€˜Xā€™ is not defined

Would you mind sharing a link to the example your trying to reproducible to help debug?

Thank you.