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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Repair Windows errors before they cause bigger problemsFix Now →Use Python’s minus operator (-) between two numbers: 10 - 3 evaluates to 7. You can print the result directly or save it in a variable.
Subtract numbers with the minus operator
In an expression such as a - b, Python subtracts the right operand (b) from the left operand (a). The Python tutorial describes the interpreter as a simple calculator: you can enter an expression and it displays the value.
print(8 - 5) # 3
remaining = 10 - 3
print(remaining) # 7Use the expression directly when you only need to display or pass along the result. Assign it to a variable when you need to use that result later.
Subtract variables and understand grouping
Variables work the same way as literal numbers: put the variable holding the amount to subtract on the right side of -.
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total = 20
spent = 7
remaining = total - spent
print(remaining) # 13Python follows operator precedence: multiplication is evaluated before subtraction. Parentheses change the grouping when you want another order. The tutorial’s examples show the difference:
print(50 - 5 * 6) # 20: 5 * 6 is evaluated first
print((50 - 5) * 6) # 270: parentheses group subtraction firstWhy subtraction may return an integer or a float
When both operands are integers, subtraction produces an integer. If an expression includes a float, the result may be a float instead; for example, 4 * 3.75 - 1 evaluates to 14.0. A displayed result ending in .0 is therefore often a consequence of using a float operand, not a different subtraction operator. See the built-in numeric types documentation.
print(8 - 5) # 3
balance = 20.50 - 7.25
print(balance) # 13.25Handle decimal precision when needed
Python’s built-in float values use binary representation, so many decimal fractions cannot be represented exactly. A result can consequently contain a small difference in its final decimal places. This is a property of floating-point representation, not a flaw in subtraction. For comparisons involving approximate float results, use a suitable tolerance rather than expecting arbitrary decimal calculations to match exactly. The floating-point arithmetic tutorial explains the issue.
For decimal-oriented arithmetic—such as values entered as money—use Decimal and construct values from strings:
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Repair Windows errors before they cause bigger problems3Scan for outdated or missing drivers - takes under a minutefrom decimal import Decimal
change = Decimal("1.10") - Decimal("0.20")
print(change) # 0.90The Decimal documentation explains that decimal inputs can be represented exactly and that subtraction can preserve fixed-point scale from the operands. Keep the operands in a consistent numeric type: combining Decimal with a float in arithmetic generally raises a TypeError.
Choose the numeric type for the calculation
- Integers: Use for whole-number arithmetic.
- Floats: Use for ordinary calculations where a small binary approximation is acceptable.
- Decimal: Use for decimal-oriented calculations when decimal representation, precision, or rounding control matters.
- Fractions: Use
Fractionwhen rational values need exact representation and it suits the calculation.
Python documents these numeric types and their behavior in the built-in types reference and the Decimal module documentation.
Quick Recap
Fix common subtraction problems
- The result ends in
.0: Check whether one operand is a float; mixed arithmetic can produce a float result. - The last decimal digits look unexpected: The expression may use floats, which approximate many decimal fractions. Use a tolerance for approximate comparisons or consider
Decimalfor decimal arithmetic. DecimalraisesTypeError: Check that you are not mixing aDecimaland afloat. Convert or construct both operands as a consistent type.- The answer reflects an unexpected order: Add parentheses to make the intended grouping explicit.
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