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Python Basics

Python Conditions & Comparison Operators

1. What is a Condition?

  • An expression that evaluates to True or False
  • Built using comparison operators applied to operands
  • Essential for if statements and conditionals (covered in next lessons)
con = 2 == 3     # False  (2 is not equal to 3)
con = 3 == 3     # True

Important distinction: - = → assignment operator (stores a value in a variable) - == → comparison operator (checks if two values are equal)

2. The 6 Comparison Operators

Operator Meaning Example Result
== Equal to 3 == 3 True
!= Not equal to 3 != 4 True
< Less than 5 < 9 True
> Greater than 5 > 9 False
<= Less than or equal to 9 <= 9 True
>= Greater than or equal to 9 >= 10 False
  • All operators work with both int and float
  • Arithmetic is evaluated before comparison
x = 9
x + 2 > 9.5     # True  (11 > 9.5)

3. Comparing int and float

  • == between int and float compares numeric value, not type
3.0 == 3      # True  (same numeric value)
3.0 != 3      # False
  • <, >, <=, >= also work fine between int and float

4. Comparing Strings

Equality

  • Comparison is case-sensitive and space-sensitive
"hello" == "hello"    # True
"hello" == "Hello"    # False  (capital H differs)
"hello" == "hello "   # False  (trailing space differs)

Less Than / Greater Than with Strings

  • Strings are compared using their ASCII (ordinal) values character by character
  • Compare first characters → if equal, move to next → and so on
"a" < "b"     # True   (97 < 98)
"a" < "B"     # False  (97 > 66 — lowercase > uppercase)
"AC" < "Ab"   # True   (A==A, then C=67 vs b=98, so AC < Ab)

Key rule: Uppercase letters always have lower ASCII values than lowercase letters

5. ASCII Values — ord() and chr()

Every character on your keyboard has a unique numeric value called its ASCII / ordinal value

ord(character) — character → number

ord('a')    # 97
ord('A')    # 65
ord('!')    # 33

chr(number) — number → character

chr(76)     # 'L'
chr(98)     # 'b'

Key ASCII Reference Points

Character ASCII Value
'A' (uppercase) 65
'B' 66
'a' (lowercase) 97
'b' 98

Uppercase always starts at 65, lowercase at 97 — so uppercase < lowercase always

6. Comparing Mixed Types

Comparison Result Reason
"6" == 6 False Different types — not equal
"6" != 6 True Different types
"6" < 6 ❌ TypeError Can't use < / > between str and int
True == 1 True True is numerically 1
False == 0 True False is numerically 0
False == "" False Different types
True == "True" False Different types

Rule: == and != work between any types (just checks equality). <, >, <=, >= only work between compatible types (int/float with int/float, or str with str)

7. Using Variables in Conditions

x = 5
y = 9
print(x == y)     # False
print(x != 9)     # True
print(x < y)      # True

8. String Comparison — Worked Example

str1 = "ABc"
str2 = "ABC"

str1 <= str2
# A == A → move on
# B == B → move on
# c (99) vs C (67) → c > C
# So str1 is NOT <= str2 → False

str1 > str2       # True  (lowercase c > uppercase C)

9. Key Takeaways & Recap

  1. A condition is any expression that evaluates to True or False
  2. = assigns, == compares — never mix them up
  3. Six comparison operators: ==, !=, <, >, <=, >=
  4. int vs float comparisons work fine — compares numeric value
  5. String comparison is case-sensitive and uses ASCII values
  6. Uppercase letters (start at 65) are always less than lowercase (start at 97)
  7. ord() gives ASCII value of a character; chr() gives character from ASCII value
  8. == / != work across types; < / > between str and int raises TypeError