Copyright: Attribution, allow others to create paper-based, and must distribute paper (based on the original license agreement with the same license Creative Commons )
Tip "×× is not defined", a variable is not defined. Take a look at the variable is not misspelled, look at the definition is not a problem.
Sometimes a glance spelling errors may not come out, scratching, hard to understand, in fact, the error is particularly simple. Such as:
"Stratified":income_cat_proportions(strat_test_sert) #sert拼写错误，应该是set
trian_set #拼写错误trian，应该是train
Summary sustained various spelling error prone