CBSE Class 12 Computer Science: Review of Python NCERT Solutions

To use the specified functions, you need to import the following Python library modules:

1. For the load() function, which is used for deserializing objects, you need to import the pickle module.
2. For the pow() function, which calculates the power of a number (base raised to an exponent), you need to import the math module.

The specified functions belong to the following Python modules:

1. The uniform() function, used for generating random floating-point numbers within a specified range, belongs to the random module.
2. The fabs() function, which returns the absolute value of a floating-point number, belongs to the math module.

The round() and floor() functions in Python are used for numerical rounding, but they operate differently:

• round(number): This function returns the number rounded to the nearest integer. If the fractional part is exactly 0.5, it rounds to the nearest even integer (in Python 3). For example:
  • round(5.8) returns 6.
  • round(4.1) returns 4.
  • round(5.5) returns 6.
  • round(4.5) returns 4.
• floor(number): This function returns the largest integer less than or equal to the given number. It always rounds down towards negative infinity. For example:
  • floor(6.9) returns 6.
  • floor(5.01) returns 5.
  • floor(-5.1) returns -6.

In summary, round() aims for the closest integer, while floor() consistently rounds down.

Identifiers in Python must follow specific rules: they must start with a letter or an underscore, can contain alphanumeric characters and underscores, and cannot be Python keywords. They are also case-sensitive. Based on these rules, the following identifiers cannot be used for naming variables or functions:

• Total * Tax: Contains an invalid character (*), which is an operator.
• While: This is a Python keyword (used for loops). Keywords cannot be used as identifiers.
• 3rd Row: Starts with a number (3) and contains a space, both of which are invalid.
• finally: This is a Python keyword (used in exception handling).

The valid identifiers from the list are Class (though it's a keyword, it can sometimes be used if not conflicting, but generally discouraged for variables/functions), Switch (if not a reserved keyword in a specific context, but generally avoided), Column 31, and Total.

To use the specified functions, you need to import the following Python library modules:

1. For the sqrt() function, which calculates the square root of a number, you need to import the math module.
2. For the dump() function, used to serialize (save) a Python object to a file, you need to import the pickle module.

Based on Python's identifier naming rules, the following are invalid for variables or functions:

• Price*Qty: Contains an invalid operator character (*).
• float: This is a built-in data type name and a keyword in Python, hence it cannot be used as a variable or function name.
• Address one: Contains a space, which is not allowed within an identifier.
• do: This is a reserved keyword in Python and cannot be used as an identifier.

Valid identifiers from the list include Cost, switch (though often a keyword in other languages, it's not a strict reserved keyword in Python in the same way as 'if' or 'for', but using keywords is bad practice), Delete, and Number12.

The following identifiers are invalid for naming variables or functions in Python due to violations of naming rules:

• Days * Rent: Contains an invalid operator (*).
• For: This is a reserved keyword in Python used for loops.
• Grand Total: Contains a space, which is not permitted in identifiers.
• do: This is a reserved keyword in Python.
• 2Clients: Identifiers cannot begin with a digit.
• My city: Contains a space.

Valid identifiers from the list are A_price and Participantl.

The functions/methods required for the specified tasks are:

1. To find the second occurrence of a substring (like 'm' in 'madam'), you can use the string's find() or index() method. To find the *second* occurrence, you would first find the first occurrence and then search again starting from the position immediately after the first one. For example, to find the second 'm' in 'madam':
   1. Find the first 'm': 'madam'.find('m') returns 0.
   2. Search again starting from index 1: 'madam'.find('m', 1) returns 2.
   So, the method used is find() (or index()).
2. To get the position (index) of an item in a list, you use the list's index() method. For example, if you have a list my_list = ['a', 'b', 'c', 'b'], my_list.index('b') will return 1 (the index of the first occurrence of 'b').