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GroceryFrequency is the core class in corner_grocer.py, encapsulating in-memory frequency storage using collections.defaultdict. It reads a plain-text grocery purchase log, accumulates per-item counts in memory, and exposes methods for lookups, sorted output, and ASCII histograms. This class is used by the file-based (non-database) version of Corner Grocer and works alongside the helper functions in grocery_utils.py.

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Instantiation

from collections import defaultdict
import grocery_utils as utils

# GroceryFrequency is defined in corner_grocer.py
grocery = GroceryFrequency()
grocery.process_input_file('grocery_frequency_input.txt')

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Methods

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__init__

def __init__(self)
Initializes the GroceryFrequency instance by creating an empty defaultdict(int) for frequency storage. No file I/O is performed at construction time — the dictionary is populated lazily by calling process_input_file. Parameters: None Returns: A new GroceryFrequency instance with self.frequency set to an empty defaultdict(int). 
grocery = GroceryFrequency()
print(grocery.frequency)  # defaultdict(<class 'int'>, {})

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process_input_file

def process_input_file(self, filename)
Opens the given text file, reads it line by line, normalizes each line to lowercase, and increments the corresponding counter in self.frequency. Empty lines (after stripping) are ignored. If the file does not exist, the method prints an error message and terminates the process with sys.exit(1).
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filename
str
required
Path to the input text file. Each non-empty line should contain exactly one item name. The file is read in the default system encoding.
Returns: None. Populates self.frequency in place. Error handling: Catches FileNotFoundError. Prints Error: File '{filename}' not found. and exits with status code 1. 
grocery = GroceryFrequency()
grocery.process_input_file('grocery_frequency_input.txt')

# After loading, self.frequency contains normalized lowercase keys
print(grocery.frequency['apples'])  # e.g. 4

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lookup_item_frequency

def lookup_item_frequency(self, item)
Returns the purchase count for a single item. The item string is normalized to lowercase before the lookup so that 'Apples', 'APPLES', and 'apples' all resolve to the same key. Returns 0 if the item has never been seen.
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item
str
required
The item name to look up. Case-insensitive.
Returns: int — the number of times the item appeared in the input file, or 0 if not found. 
grocery = GroceryFrequency()
grocery.process_input_file('grocery_frequency_input.txt')

count = grocery.lookup_item_frequency('Apples')
print(f"Apples were purchased {count} time(s).")
# Apples were purchased 4 time(s).

missing = grocery.lookup_item_frequency('durian')
print(missing)  # 0

def print_all_frequencies(self)
Iterates over all keys in self.frequency sorted alphabetically (A–Z) and prints each item along with its count in the format item: count. Output is written directly to stdout. Parameters: None Returns: None 
grocery = GroceryFrequency()
grocery.process_input_file('grocery_frequency_input.txt')
grocery.print_all_frequencies()
# apples: 4
# bananas: 3
# carrots: 2

def print_histogram(self)
Iterates over all keys in self.frequency sorted alphabetically (A–Z) and prints each item followed by a string of asterisks whose length equals the item’s count. This provides a visual bar chart in the terminal. Output is written directly to stdout. Parameters: None Returns: None 
grocery = GroceryFrequency()
grocery.process_input_file('grocery_frequency_input.txt')
grocery.print_histogram()
# apples: ****
# bananas: ***
# carrots: **

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Standalone Helper Functions

The following module-level functions are defined in corner_grocer.py outside the GroceryFrequency class. They handle menu display and user input validation for the interactive terminal application.

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get_validated_choice

def get_validated_choice()
Prompts the user with "Enter your choice: " and attempts to parse the response as an integer. Returns the integer if it falls in the range 1–7 (inclusive). Prints an error message and returns 0 for any out-of-range value or non-integer input. Parameters: None Returns: int — a valid choice in the range 1–7, or 0 on invalid input. 
choice = get_validated_choice()
if choice == 0:
    print("Re-prompting due to invalid input.")

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is_valid_item_name

def is_valid_item_name(item_name)
Validates that every character in item_name is either an alphabetic letter or a space. Rejects strings containing digits, punctuation, or other special characters.
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item_name
str
required
The item name string to validate.
Returns: bool — True if all characters pass the check, False otherwise. 
print(is_valid_item_name("green beans"))  # True
print(is_valid_item_name("item#1"))       # False
print(is_valid_item_name("açaí"))         # False (non-ASCII)

def print_menu()
Prints the seven-option Corner Grocer interactive menu to stdout and flushes the output buffer. The menu includes options for item lookup, frequency display, histogram rendering, alphabetical sort, frequency sort, item search, and program exit. Parameters: None Returns: None 
print_menu()
# ========== Corner Grocer Menu ==========
# 1. Look up item frequency
# 2. Print all items and frequencies
# 3. Print frequency histogram
# 4. Sort items alphabetically (A–Z)
# 5. Sort items by frequency (high → low)
# 6. Search for a specific item
# 7. Exit program

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