OLE DB
train_data.Embarked[train_data.Embarked.isnull()] = train_data.Embarked.dropna().mode().values
Fierce Fox
train_data.Embarked[train_data.Embarked.isnull()] = train_data.Embarked.dropna().mode().values
train_data[['Sex','Survived']].groupby(['Sex']).mean().plot.bar()