OAU CSC 201 Practice Quiz

cmp(x, y) returns 1 if x > y, 0 if x == y and -1 if x < y.

Python first searches for the local, then the global and finally the built-in namespace.

In the code shown above, we have not passed any parameter to the function p. Hence the output of this code is: hello.

All of the above examples show explicit conversion. However the expression int(’10.8’) results in an error.

‘.py’ is the correct extension of the Python file. Python programs can be written in any text editor. To save these programs we need to save in files with file extension ‘.py’.

The code snippet shown above results in an error because the above formatting option works only if ‘X’ is a number. Since in the above case ‘X’ is a string, an error is thrown.

True, False and None are capitalized while the others are in lower case.

The expression shown above normally returns the value with 6 decimal points if it is not specified with any number. Hence the output of this expression will be: 34.000000 (6 decimal points).

The else part is not executed if control breaks out of the loop.

^ is the XOR operator. The binary form of 4 is 0100 and that of 12 is 1100. Therefore, 0100^1100 is 1000, which is equal to 8.

eval can be used as a variable.

The code shown above shows a general decorator which can work with any number of arguments.

Understanding Arithmetic Operators with Strings:

1. * (Multiplication):
• Strings can be multiplied with integers to create repeated copies of the string.
• Example:

print(“abc” * 3) # Output: abcabcabc

• Allowed with strings.

2. – (Subtraction):
• Subtraction is not defined for strings in Python. You cannot subtract one string from another.
• Example:

print(“abc” – “a”) # This will raise a TypeError.

• Not allowed with strings.

3. + (Addition):
• Strings can be concatenated (joined) using the + operator.
• Example:

print(“abc” + “def”) # Output: abcdef

• Allowed with strings.

4. All of the mentioned:
• Since both * and + are allowed with strings, not all arithmetic operators are disallowed. Only – (subtraction) cannot be used with strings.

Correct Answer:

b) –

Subtraction (-) is the arithmetic operator that cannot be used with strings in Python.

i is not in x[1:].

Here i i i i i … printed continuously because as the value of i or x isn’t changing, the condition will always evaluate to True. But also here we use a citation marks on “i”, so, here i treated as a string, not like a variable.

The above expressions are evaluated as: 2/2, 8/2, which is equal to (1.0, 4.0).

The order of precedence is: %, +. Hence the expression above, on simplification results in 4 + 3 = 7. Hence the result is 7.

Explanation: { } creates a dictionary not a set. Only set() creates an empty set.

This is a built-in function which rounds a number to give precision in decimal digits. In the above case, since the number of decimal places has not been specified, the decimal number is rounded off to a whole number. Hence the output will be 5.

When both of the operands are integer then python chops out the fraction part and gives you the round off value, to get the accurate answer use floor division. This is floor division. For ex, 5/2 = 2.5 but both of the operands are integer so answer of this expression in python is 2. To get the 2.5 answer, use floor division.

The expression int(‘1111’,2) gives the result 15. The expression int(‘1111’, 10) will give the result 1111.

Bitwise XOR gives 1 if either of the bits is 1 and 0 when both of the bits are 1.

String x is not being altered and i is in x[:-1].

We can simply convert strings with a %s format expression or the str built-in function. Both of these methods have been shown in this code. Hence the output is: ) (‘3.3456789’, ‘3.3456789’)

All of the operators shown above have associativity from left to right, except exponentiation operator (**) which has its associativity from right to left.

Variable names can be of any length.

+ operator is concatenation operator.

The code shown above prints the values substituted for a, b, a, in the same order. This operation is performed using the format function. Hence the output of the code is: ‘helloworldhello’.

Execute help(id) to find out details in python shell.id returns a integer value that is unique.Execute help(id) to find out details in python shell.id returns a integer value that is unique.

The @ symbol can be used as an alternate way to specify a function that needs to be decorated. The output of the codes shown above is the same. Hence they are equivalent. Therefore this statement is true.

The expressions are evaluated as: 4%3 and 6//2 respectively. This results in the answer (1,3). This is because the associativity of both of the expressions shown above is left to right.

SyntaxError, True is a keyword and it’s value cannot be changed.

9 isn’t allowed in an octal number.

in is a keyword.

The code shown above shows two functions. In both the cases the right operand is returned. This is because each function is evaluated from left to right. Since the left operand is false, it is assumed that the right operand must be true and hence the right operand is returned in each of the above case.

The above expression returns the output 000345. It adds the required number of zeroes before the given number in order to make the number of digits 6 (as specified in this case).

The same object is modified in the function.

Let’s break this down step by step so that it’s clear.

Code Analysis:

The Function:

def foo(x):

    x[0] = [‘def’]  # Changes the first element of the list `x` to [‘def’]

    x[1] = [‘abc’]  # Changes the second element of the list `x` to [‘abc’]

    return id(x)    # Returns the memory address (ID) of the modified list `x`

The Main Code:

q = [‘abc’, ‘def’]          # Creates a list `q` with two elements: [‘abc’, ‘def’]

print(id(q) == foo(q))      # Compares the memory address (ID) of `q` with the value returned by `foo(q)`

Step-by-Step Explanation:

1. List q Initialization:

• A list q is created:

q = [‘abc’, ‘def’]

• This list has an ID, which is its memory address. Let’s call it id(q).

2. Calling foo(q):

• The list q is passed into the function foo.

• Inside foo:

• x[0] = [‘def’]: The first element of the list is changed to [‘def’].

Now, q looks like this:

[[‘def’], ‘def’]

• x[1] = [‘abc’]: The second element of the list is changed to [‘abc’].

Now, q looks like this:

[[‘def’], [‘abc’]]

• The id(x) is returned. Since x and q refer to the same list, id(x) is the same as id(q).

3. Comparison (id(q) == foo(q)):

• The memory address of q is compared to the memory address returned by foo(q).

• Since foo(q) does not create a new list but modifies the same list, id(q) and id(x) are identical.

Output:

True

Key Points to Understand:

1. Lists are mutable: When you pass a list to a function, any changes made to the list inside the function will affect the original list because they share the same memory address.

2. The id() function: This returns the memory address of an object.

The code shown above returns a new list containing only those elements of the list l which do not amount to zero. Hence the output is: [1, 2, ‘hello’].

Since we have specified that the order of the output be: {a}, {0}, {abc}, hence the value of associated with {a} is printed first followed by that of {0} and {abc}. Hence the output of the code shown above is: ‘2.5, 10, [1, 2]’.

l (or L) stands for long.

The expression shown above is evaluated as: 2+9*(36-8)/10, which simplifies to give 2+9*(2.8), which is equal to 2+25.2 = 27.2. Hence the result of this expression is 27.2.

As Python has no concept of private variables, leading underscores are used to indicate variables that must not be accessed from outside the class.

The instance of the string returned by upper() is being printed.

As the value of i or x isn’t changing, the condition will always evaluate to True.

A folder of python programs is called as a package of modules.

In the code shown above, we have used a decorator in order to avoid the Zero Division Error. Hence the output of this code is:

    hello
    NO

We use the function append to add an element to the list.