why to use train test split code example

Example 1: code for test and train split

from sklearn.model_selection import train_test_split
X_train, X_test, y_train, y_test = train_test_split(
 X, y, test_size=0.33, random_state=42)

Example 2: train test split

from sklearn.linear_model import LinearRegression

rl = LinearRegression().fit(X, y)
rl.fit(X, y) #We can fit model to dataset in this way too