There are variables X_train, X_test, y_train, y_test created through sklearn train_test_split. They contain text data in string format. Convert them to float numbers.

from sklearn import datasets
import numpy as np

X, y = datasets.load_svmlight_file('data.txt')
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.33, random_state=42)
X_train = X_train.toarray()
X_test = X_test.toarray()
y_train = y_train.astype('float')
y_test = y_test.astype('float')