Converting Between Data Types: An Overview
float() converts integers and numeric strings to floating-point numbers, adding decimal representation where none existed.
From Whole Numbers to Decimal Form
A value can be represented in more than one data type. The float() conversion changes an integer or a numeric string into a floating-point number. When an integer has no decimal representation, float() adds one to the representation while preserving the number's quantity.
7.0Tracing Numeric Strings
User input commonly arrives as a string, even when the user typed a number. float() can convert a string representation of a number into a floating-point number. For example, the numeric string "3.14" becomes the floating-point value 3.14. The important condition is that the string must represent a valid number.
Converting a Numeric String
Convert the numeric string "3.14" into a floating-point number.
Start with the string: The input is a string representation of a number rather than a numeric value already stored as a number.
Apply float(): float() reads the valid numeric string and converts it to floating-point form.
Read the result: The resulting numeric value is represented as 3.14.
float("3.14") produces 3.14 as a floating-point number.
3.14float() and int() Compared
The key difference is what happens to a fractional part. float() preserves fractional values and returns a true floating-point type. int(), by contrast, truncates a value when converting it to an integer. Therefore, choosing between the two conversions depends on whether the fractional part must remain available.
| Conversion | Behavior with a fractional value | Resulting form |
|---|---|---|
| float() | Preserves the fractional value | Floating-point number |
| int() | Truncates the fractional value | Integer |
Predicting Conversion Results
What do you think happens?
What happens when float() receives each of these inputs?
Reveal answer
Answer: float(7) returns 7.0. float("3.14") returns 3.14. float("not a number") raises a ValueError because the string does not represent a valid number.
Integers and valid numeric strings can be converted to floating-point numbers. An input string that is not a valid number cannot be converted by float().
Mistakes Beginners Make
Assuming float() removes the fractional part.
float() preserves fractional values.
Fix:
Use float() when the fractional part must remain available. int() is the conversion described as truncating.Treating every string as convertible.
The string does not represent a valid number, so float() raises a ValueError.
Fix:
Provide a string representation of a valid number before using float().Forgetting that float() changes the data type.
float() returns a true floating-point type.
Fix:
Remember that 7 becomes the floating-point representation 7.0.
Choosing the Conversion
Use float() when a calculation needs values in floating-point form or when a numeric value arrives as a string and its fractional part should be preserved. This is especially useful when handling user input represented as strings. Use int() instead when the intended behavior is truncation and an integer result is required.
For each input, predict the result of float(): float(12), float("8.5"), and float("eight"). Then identify which input causes a ValueError.
Hints
- An integer is converted to floating-point form with decimal representation.
- A valid numeric string can be converted.
- A string that does not represent a valid number causes a ValueError.
Key Takeaways
- float() converts integers and valid numeric strings to floating-point numbers.
- Converting an integer adds decimal representation, such as 7 becoming 7.0.
- float() preserves fractional values, while int() truncates them.
- An invalid numeric string causes float() to raise a ValueError.
- float() is useful for converting string-based user input and for ensuring values are in floating-point form for calculations.
Key Takeaways
- float() converts integers and numeric strings into floating-point numbers.
- An integer such as 7 is represented as 7.0 after conversion.
- float() preserves fractional values, unlike int(), which truncates them.
- Invalid numeric strings cause float() to raise a ValueError.