Sklearn logistic regression, plotting probability curve graph

you use predict(X) which gives out the prediction of the class. replace predict(X) with predict_proba(X)[:,1] which would gives out the probability of which the data belong to class 1.

You can use seaborn regplot with the following syntax

import seaborn as sns
sns.regplot(x='balance', y='default', data=data, logistic=True)