Python Basics: Data Types, Operators and Type Conversion (ISC Class 11)

Understand Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion

a = [1, 2, 3]
b = a            # same object
b.append(4)
print(a)         # [1, 2, 3, 4]

Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion: key facts

Division operators

• •a / b: float
• •a // b: floor of the quotient
• •a % b = a - b x (a // b)

Check the sign.

Precedence

• •Power first
• •multiply, divide, floor-divide, remainder
• •add, subtract
• •comparisons
• •not
• •and
• •or

Left to right at the same level; power goes right to left.

Conversions

• •int(3.9) = 3
• •float(7) = 7.0
• •str(5) = '5'
• •bool(0) = False

Explicit casting.

How to answer Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion questions

1. 1Mark the operators and their precedence.
2. 2Evaluate the highest first; at the same level go left to right (power right to left).
3. 3Track the type: int, float, str, bool.
4. 4For lists, track aliases (two names for one object).

Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Tricks to remember Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion

Short memory aids. Say each one aloud once, then use it on a question the same day.

• Floor goes down

  -17 // 5 is -4, not -3.

  Use it when: //.

• Remainder takes the divisor's sign

  -17 % 5 is 3; 17 % -5 is -3.

  Use it when: %.

• Power from the right

  2 3 2 is 2 ** 9 = 512.

  Use it when: **.

Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Where students lose marks in Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion

The slips examiners see most often, and what to write instead.

• ✗Mistake: Truncating instead of flooring negative numbers

  C habit.

  Wrong working

  -17 // 5 = -3

  Right working

  -4

  ✓Do this: // floors.

  Usually costs: 1-2 marks.

• ✗Mistake: Reading input() as a number

  Forgetting conversion.

  Wrong working

  n = input(); n * 2 with n = 7 gives 14

  Right working

  n = '7'; n * 2 = '77'

  ✓Do this: Use int(input()).

  Usually costs: 2 marks.

• ✗Mistake: Left-to-right power

  Same level rule.

  Wrong working

  2 3 2 = 64

  Right working

  512

  ✓Do this: ** is right-associative.

  Usually costs: 1-2 marks.

Practice questions on Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQBoard level

   The data type of the result of 7 / 2 in Python 3 is:
   (a) int (b) float (c) str (d) bool

   Hint

   True division.

   Answer

   (b) float (the value is 3.5)

2. Q2 · 2 marks · Short answerBoard level

   Give the output: x = 14; y = 4; print(x // y, x % y, x / y, x ** 2 % 10) (2 marks)

   Hint

   196 % 10.

   Answer

   3 2 3.5 6

3. Q3 · 6 marks · Long answerHarder board level

   Evaluate and show steps: (a) 10 - 4 * 2 ** 2 // 3 (b) not 3 > 5 or 2 == 2 and 1 > 3 (c) 7 // 2 * 2 + 7 % 2 (d) -9 // 4 + -9 % 4. (6 marks)

   Hint

   Precedence.

   Answer

   (a) 2 ** 2 = 4; 4 * 4 = 16; 16 // 3 = 5; 10 - 5 = 5. (b) 3 > 5 is False; not False is True; the right part: 2 == 2 is True and 1 > 3 is False gives False; True or False = True. (c) 7 // 2 = 3; 3 * 2 = 6; 7 % 2 = 1; 6 + 1 = 7. (d) -9 // 4 = -3; -9 % 4 = 3; sum 0.

4. Q4 · 4 marks · Short answerHarder board level

   A program reads two numbers as strings: a = input() and b = input() with the user typing 12 and 30. Give the output of print(a + b), print(int(a) + int(b)) and print(a * 2), and fix the first to give 42. (4 marks)

   Hint

   String concatenation.

   Answer

   1230; 42; 1212. To get 42, convert: print(int(a) + int(b)).

5. Q5 · 3 marks · Short answerHOTS / competency

   A student writes: scores = [40, 50]; copy = scores; copy[0] = 99; print(scores). She expected [40, 50]. Give the output, the reason, and two ways to make a true copy. (3 marks)

   Hint

   Alias.

   Answer

   Output: [99, 50]. copy = scores binds a second name to the same list. A true copy: copy = scores.copy() or copy = scores[:] (also list(scores)).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1./ always gives?Show answer

   float.

2. 2.// rounds?Show answer

   Down (floor).

3. 3.Mutable types?Show answer

   list, dict, set.

4. 4.input() returns?Show answer

   A string.

5. 5.Power associativity?Show answer

   Right to left.

Python: Tokens, Variables, Data Types, Operators, Precedence and Type Conversion: frequently asked questions