Summary  
This chapter demonstrates using the string.find(substring) method to locate the index of the first occurrence of a given character or substring in a string, returning -1 if it’s not found.

General domain of usage  
Text processing

To find the index of a specific symbol or substring in a string, Python provides the built-in `.find()` method. This method returns the index of the first occurrence of the substring. If the substring is not found, it returns -1.

```python
string.find(substring)
```
Here, string is the original text, and substring is the character or sequence you want to locate.

string = "Channel efforts to success!"
print(string.find('n'))

In the string `"Channel efforts to success!"`, the first `'n'` appears at index 3. So, the `find()` method returns 3.

If the character were not found, for example, `string.find('z')`, the result would be -1.

import unittest
import sys
from io import StringIO


class TestUserCode(unittest.TestCase):
    def _test_variable_equals_string(self, var_name, expected):
        import user_code
        if not hasattr(user_code, var_name):
            return (False, f"Expected '{var_name}' variable to be defined.")
        var = getattr(user_code, var_name)
        if var != expected:
            return (False, f"Expected '{var_name}' to equal '{expected}', but got '{var}'.")
        return (True, f'The variable {var_name} equals "{expected}"')

    def test_p(self):
        passed, result_text = self._test_variable_equals_string(
            'p', 15)
        self._testMethodName = result_text
        self.assertTrue(passed, result_text)

    def test_y(self):
        passed, result_text = self._test_variable_equals_string(
            'y', 5)
        self._testMethodName = result_text
        self.assertTrue(passed, result_text)

    def test_r(self):
        passed, result_text = self._test_variable_equals_string(
            'r', 2)
        self._testMethodName = result_text
        self.assertTrue(passed, result_text)


if __name__ == '__main__':
    unittest.main()


test_main.py

Gain a solid understanding of Python's core data types and learn how to work with them effectively. Explore numbers, booleans, and strings through hands-on exercises and practical examples. Build confidence in performing basic operations and develop the foundational skills needed to write clean and efficient Python code.

Discover the essentials of numerical data types in Python and learn how to work with integers and floating-point numbers. Master basic arithmetic operations, explore the concept of immutability, and get hands-on experience using Python's built-in functions and tools to handle numbers efficiently in real-world scenarios.

Gain a clear understanding of the Boolean data type, a specialized subtype of numeric data that represents truth values. Although it may seem challenging at first, mastering Booleans is essential for writing logical and efficient programs. This section will help you confidently apply Boolean logic to real-world programming scenarios.

Strings allow you to work with text in Python, from displaying messages to processing user input. You'll explore how to create, modify, and manipulate strings effectively. Understanding strings is essential for writing interactive programs and communicating information clearly through your code.

Learn how to handle data types effectively to ensure accuracy and consistency in your programs. Convert values to the appropriate type, clean text before comparison, and separate numeric operations from text formatting. You'll also discover how to manage missing data deliberately and handle human-readable text differently from raw input, achieving reliable, consistent, and easy-to-read results.

Get the Index of the Symbol

解答