convert dataframe to dictionary without values in python code example

Example 1: dataframe to dict without index

{'Name': ['John', 'Sara', 'John', 'Sara'],
 'Sem': ['Sem1', 'Sem1', 'Sem2', 'Sem2'],
 'Subject': ['Mathematics', 'Biology', 'Biology', 'Mathematics'],
 'Grade': ['A', 'B', 'A+', 'B++']}

Example 2: dataframe to dict without index

{0: {'Name': 'John', 'Age': 38, 'City': 'Boston'},
 1: {'Name': 'Sara', 'Age': 47, 'City': 'Charlotte'},
 2: {'Name': 'Peter', 'Age': 63, 'City': 'London'},
 3: {'Name': 'Cecilia', 'Age': 28, 'City': 'Memphis'}}