1. Function Overview
<span>range</span> is a built-in function in Python that generates an immutable sequence of integers, commonly used for loop control, index generation, or data serialization. Its core features include:
- • Lazy Generation: Does not generate the complete sequence immediately, but computes it on demand, saving memory.
- • Efficiency: Suitable for handling large ranges of numbers (e.g., in the millions) with very low memory usage.
- • Flexibility: Supports operations such as ascending, descending, and custom step sizes.
2. Function Prototype
The syntax of <span>range</span> has two forms:
range(stop)
range(start, stop[, step])Parameters:
- •
<span>start</span>(optional): The starting value of the sequence, defaulting to<span>0</span>. - •
<span>stop</span>(required): The ending value of the sequence (not inclusive). - •
<span>step</span>(optional): The step size, defaulting to<span>1</span>.
3. Parameter Analysis
| Parameter | Type | Description |
<span>start</span> |
Integer | The starting value; if not specified, it starts from <span>0</span>. If <span>stop</span> is specified but <span>start</span> is not, then <span>start</span> defaults to <span>0</span>. |
<span>stop</span> |
Integer | The ending value (not inclusive), must be specified. For example, <span>range(5)</span> generates <span>0-4</span>. |
<span>step</span> |
Integer | The step size, which can be positive (incrementing) or negative (decrementing). If not specified, it defaults to <span>1</span>. If it is <span>0</span>, a <span>ValueError</span> will be raised. |
Note:
- • If
<span>step</span>is negative,<span>start > stop</span>must be satisfied; otherwise, an empty sequence is returned. - • Parameters must be integers; floating-point numbers are not supported.
4. Return Value
Returns a <span>range</span> object (an immutable sequence), which can be converted to a list using <span>list()</span> to view specific values.
Features:
- • Supports iteration, slicing, and membership testing (using the
<span>in</span>operator). - • Supports negative indexing (e.g.,
<span>range(10)[-1]</span>returns<span>9</span>). - • Memory usage is fixed, only storing the three parameters:
<span>start</span>,<span>stop</span>, and<span>step</span>.
5. Examples
Example 1: Basic Usage
# Generate a sequence from 0 to 4
print(list(range(5))) # Output: [0, 1, 2, 3, 4]
# Generate a sequence from 5 to 9
print(list(range(5, 10))) # Output: [5, 6, 7, 8, 9]Example 2: Specifying Step Size
# Generate odd numbers from 1 to 9
print(list(range(1, 10, 2))) # Output: [1, 3, 5, 7, 9]
# Generate even numbers in reverse from 10 to 2
print(list(range(10, 1, -2))) # Output: [10, 8, 6, 4, 2]Example 3: Using with Loops
# Iterate over indices
data = ["a", "b", "c"]
for i in range(len(data)):
print(f"Index {i}: {data[i]}")Example 4: Efficiently Handling Large Ranges
# Generate a range object of 1 million numbers (very low memory usage)
larg_range = range(10**6)
print(len(larg_range)) # Output: 1000000Conclusion
<span>range</span> is a core tool in Python for efficiently generating integer sequences. With its lazy characteristics and flexible parameter configurations, it can be widely applied in loop control, data generation, and other scenarios. By converting with <span>list()</span> or using it directly in iteration, it can meet various needs.