Computer Science
Grade 8
20 min
Finding Letters and Numbers
Finding Letters and Numbers
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1
Introduction & Learning Objectives
Learning Objectives
Utilize built-in string methods to locate specific characters or substrings within text data.
Construct and interpret basic regular expressions to define complex search patterns for letters and numbers.
Apply iterative algorithms to search for alphanumeric patterns within lists or arrays of strings.
Implement conditional logic to differentiate between various character types (alphabetic, numeric, special) in a given string.
Develop functions to validate user input for specific letter and number formats, mimicking web form validation.
Analyze the efficiency of different search methods for finding letters and numbers in various data structures.
Ever wonder how websites instantly tell you if your password is strong enough or if you typed your email correctly...
2
Key Concepts & Vocabulary
TermDefinitionExample
StringA sequence of characters, such as letters, numbers, and symbols, treated as a single data type.The variable `product_name = "Laptop Pro X1"` stores a string.
Character SetA defined list of characters that a computer can recognize and process, like ASCII or Unicode, each having a unique numerical representation.In ASCII, the character 'A' is represented by the number 65, and '1' by 49.
Regular Expression (Regex)A powerful sequence of characters that defines a search pattern, often used for 'find and replace' operations or input validation.`\d+` is a regex that matches one or more digits (numbers), useful for finding all numbers in a text.
Pattern MatchingThe process of checking a sequence of characters (a string) for the p...
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Core Syntax & Patterns
String `find()` / `index()` Methods
`string.find(substring, start, end)` returns the lowest index in the string where `substring` is found. Returns -1 if not found. `string.index()` is similar but raises an error if not found.
Use these methods to quickly locate the starting position of a specific sequence of letters or numbers within a larger string. They are ideal for simple, exact matches and are commonly used in many programming languages.
Basic Regular Expression Character Classes
Special sequences for matching character types:
- `\d`: Matches any digit (0-9).
- `\w`: Matches any alphanumeric character (letters, numbers, and underscore).
- `[a-zA-Z]`: Matches any uppercase or lowercase letter.
- `[0-9]`: Matches any digit (same as `\d`).
These special sequences allow yo...
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Challenging
You need to write a function that validates product codes from a list. A valid code must match the exact format 'PROD-[A-Z]{3}-\d{5}-[A-Z]{1}'. Which function correctly identifies and returns only the valid codes?
A.function that uses `code.find('PROD-')` and then checks the length.
B.function that iterates, uses `re.match(r'^PROD-[A-Z]{3}-\d{5}-[A-Z]{1}$', code)` for each code, and appends matches to a new list.
C.function that joins the list into one string and uses `re.findall(r'PROD-\w{3}-\d{5}-\w{1}')`.
D.function that checks if 'PROD', 3 letters, 5 numbers, and 1 letter exist anywhere in the string using `re.search()`.
Challenging
When tasked with extracting all integer prices (e.g., '199', '25') from a large, messy block of web-scraped text, which search method provides the best balance of accuracy and performance?
A.Iterating character by character, checking `char.isdigit()`, and manually building number strings.
B.Using `string.find()` repeatedly to search for each digit '0' through '9'.
C.single call to a regex function like `re.findall(r'\d+')`.
D.Splitting the text by spaces and trying to convert each word to an integer inside a try-except block.
Challenging
Synthesize a regular expression that validates a Canadian postal code in the format 'A1A 1A1' (Letter-Digit-Letter, a single space, then Digit-Letter-Digit).
A.`^[A-Z]\d[A-Z] \d[A-Z]\d$`
B.`[A-Z]\d[A-Z]\s[A-Z]\d[A-Z]`
C.`\w\d\w\s\d\w\d`
D.`([A-Z]\d){3}`
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