Python PCEP-30-02 Certification Preparation

• ata1 = '1', '2':

  • This line creates a tuple named data1.
  • The comma is what defines it as a tuple, not the absence or presence of parentheses!
  • data1 is equivalent to ('1', '2') which is a tuple containing two string elements: '1' and '2'.

• data2 = ('3', '4'):

  • This line explicitly creates a tuple named data2 using parentheses.
  • data2 contains two string elements: '3' and '4'.

• print(data1 + data2):

  • The + operator, when used with tuples, performs tuple concatenation. It creates a new tuple by joining the elements of the two tuples.
  • In this case, it joins the elements of data1 and data2.

An interpreter reads the source code instruction by instruction, executing each line immediately. Unlike a compiler, it doesn't create a separate executable file.

0 in list: This expression uses the in operator to check if the value 0 (the integer zero) is present as an element within the list.

False is equivalent to 0 in Python. Because False is equivalent to 0 in Python and False is an element in the list, the expression 0 in list evaluates to True.

A compiler processes the whole program upfront, creating an executable. An interpreter goes through the code line by line, executing as it goes.

1. list1 = [1, 3]: A list named list1 is created, containing the elements 1 and 3.

2. list2 = list1: This is a crucial step. It does not create a new list. Instead, list2 becomes a reference (or alias) to the same list object that list1 is referencing. Both list1 and list2 now point to the same memory location where the list [1, 3] is stored.

3. list1[0] = 4: This modifies the element at index 0 of the list that list1 is referencing. Since list1 and list2 both point to the same list, this change is visible through both variables.

4. print(list2): This prints the list that list2 is referencing. Because list1 modified the list, list2 will reflect that change.

The def keyword is how you define a function in Python. It signals to the interpreter that you are about to create a new, reusable block of code.

1. my_list = [3, 1, -1]: A list named my_list is created with the initial values 3, 1, and -1.

2. my_list[-1] = my_list[-2]: This line modifies the list by assigning a new value to one of its elements:

   • my_list[-1] refers to the last element of the list (which is currently -1).
   • my_list[-2] refers to the second-to-last element of the list (which is currently 1).
   • The assignment my_list[-1] = my_list[-2] copies the value of the second-to-last element (1) and assigns it to the last element. In effect, it replaces -1 with 1.

After this assignment, the list my_list becomes [3, 1, 1].

1. a = [1, 2, 3, 4, 5, 6, 7, 8, 9]: This creates a list named a containing the integers from 1 to 9.

2. print(a[::2]): This line uses list slicing to extract and print a subset of the list.

   • a[start:stop:step] is the general form of list slicing. When start and stop are omitted, they default to the beginning and end of the list, respectively.
   • In this case, a[::2] means:
     • Start at the beginning of the list (the default start is 0).
     • End at the end of the list (the default stop is the end of the list).
     • Take every second element (the step is 2).

The slice will therefore select the elements at indices 0, 2, 4, 6 and 8.

In Python, you can define strings using either single quotes ('...') or double quotes ("..."). Both are perfectly valid and equivalent.