Practice: Files, JSON, and Paths¶

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Five practice problems, one per concept step. The numbers line up. Build each yourself, then check python-practice/solutions. Some end with a short input() "Write a Program" exercise. Each file tidies up after itself with .unlink().

These problems continue the online store story: now you are SAVING the work to disk. You write and read back the catalog, keep an orders log, save and load a product and a cart item as JSON, and inspect the path of a catalog file.

Step-01: Write a Text File, Then Read It Back¶

Concepts: with open(...), "w", "r", encoding="utf-8", .unlink().

Problem-1: Save the Catalog.

Write a program that writes the two catalog lines Wireless Mouse - 25 and Mechanical Keyboard - 45 to store_catalog.txt, reads the whole file back as one string and prints it, removes the file, then prints the done message Saved the catalog, read it back, then removed it.

Wireless Mouse - 25
Mechanical Keyboard - 45

Saved the catalog, read it back, then removed it.

from pathlib import Path

with open("store_catalog.txt", "w", encoding="utf-8") as f:
    f.write("Wireless Mouse - 25\n")
    f.write("Mechanical Keyboard - 45\n")

with open("store_catalog.txt", "r", encoding="utf-8") as f:
    catalog_text = f.read()
print(catalog_text)

Path("store_catalog.txt").unlink()
print("Saved the catalog, read it back, then removed it.")

Problem-2: Save the Store Name.

Write a program that writes the line Gadget Hub to store_name.txt (use encoding="utf-8"), reads it back, strips the whitespace, prints it as store: <text>, then removes the file.

store: Gadget Hub

from pathlib import Path

with open("store_name.txt", "w", encoding="utf-8") as f:
    f.write("Gadget Hub\n")

with open("store_name.txt", "r", encoding="utf-8") as f:
    print("store:", f.read().strip())

Path("store_name.txt").unlink()

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Step-02: Append Lines, Then Read Line by Line¶

Concepts: "a" append, read line by line, strip(), input().

Problem-1: Orders Log.

Write a program that writes order-1 to orders_log.txt, then appends order-2 and order-3 to the same file, then:

• Task-1: read the file line by line and print each line as order: <text> (strip the newline).
• Task-2: read the whole file again with .readlines() and print how many orders there are, as orders logged: <count>.

order: order-1
order: order-2
order: order-3
orders logged: 3

from pathlib import Path

with open("orders_log.txt", "w", encoding="utf-8") as f:
    f.write("order-1\n")
with open("orders_log.txt", "a", encoding="utf-8") as f:
    f.write("order-2\n")
    f.write("order-3\n")
with open("orders_log.txt", "r", encoding="utf-8") as f:
    for line in f:
        print("order:", line.strip())

# Problem-1 Task-2: readlines() gives the whole file as a list, so len() counts the orders
with open("orders_log.txt", "r", encoding="utf-8") as f:
    all_orders = f.readlines()
print("orders logged:", len(all_orders))

Path("orders_log.txt").unlink()

Problem-2 (Write a Program): Add an Order.

Write a program that asks the user for an order, writes Today's orders: to daily_orders.txt, appends the typed order to the same file, then reads the file back and prints it.

Enter an order: Wireless Mouse
Today's orders:
Wireless Mouse

from pathlib import Path

order = input("Enter an order: ")
with open("daily_orders.txt", "w", encoding="utf-8") as f:
    f.write("Today's orders:\n")
with open("daily_orders.txt", "a", encoding="utf-8") as f:
    f.write(order + "\n")
with open("daily_orders.txt", "r", encoding="utf-8") as f:
    print(f.read())
Path("daily_orders.txt").unlink()

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Step-03: JSON - Save and Load Structured Data¶

Concepts: json.dump, json.load, json.dumps, input().

Problem-1: Save a Product.

Write a program that saves a product dict with name set to Wireless Mouse, category set to Audio, and price set to 25 to product.json, loads it back, then (after loading) removes the file. From the loaded dict:

• Task-1: print the whole loaded dict.
• Task-2: print the name value as name is: <name>.
• Task-3: print the price value as price is: <price>.
• Task-4: turn the loaded dict into a JSON string with json.dumps() and print it, then print its type() to prove it is text and not a dict.

{'name': 'Wireless Mouse', 'category': 'Audio', 'price': 25}
name is: Wireless Mouse
price is: 25
{"name": "Wireless Mouse", "category": "Audio", "price": 25}
<class 'str'>

import json
from pathlib import Path

product = {"name": "Wireless Mouse", "category": "Audio", "price": 25}
with open("product.json", "w", encoding="utf-8") as f:
    json.dump(product, f, indent=2)
with open("product.json", "r", encoding="utf-8") as f:
    loaded_product = json.load(f)
# Problem-1 Task-1: print the whole loaded dict
print(loaded_product)
# Problem-1 Task-2: print the name value
print("name is:", loaded_product["name"])
# Problem-1 Task-3: print the price value
print("price is:", loaded_product["price"])

# Problem-1 Task-4: json.dumps turns the dict into a JSON string (text), not a file
text = json.dumps(loaded_product)
print(text)
print(type(text))
Path("product.json").unlink()

Problem-2 (Write a Program): Save a Cart Item.

Write a program that asks the user for a product, saves {"product": <product>} to cart.json, loads it back and prints it, then removes the file.

Enter a product: Keyboard
{'product': 'Keyboard'}

import json
from pathlib import Path

chosen = input("Enter a product: ")
cart_item = {"product": chosen}
with open("cart.json", "w", encoding="utf-8") as f:
    json.dump(cart_item, f)
with open("cart.json", "r", encoding="utf-8") as f:
    print(json.load(f))
Path("cart.json").unlink()

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Step-04: Paths with pathlib¶

Concepts: Path joining with /, .name/.suffix/.stem/.parent, write_text()/read_text(), .exists().

Problem-1: Catalog File Path.

Write a program that builds a variable catalog_path by joining the parts catalog, app_files, and products.json into one Path with the / operator. Then, for that path:

• Task-1: print the path itself.
• Task-2: print the path's name (use .name).
• Task-3: print the path's suffix (use .suffix).
• Task-4: print the path's stem (use .stem).
• Task-5: print the path's parent (use .parent).
• Task-6: print whether the path exists (use .exists(); this path was never created, so it is False).

catalog/app_files/products.json
products.json
.json
products
catalog/app_files
False

from pathlib import Path

catalog_path = Path("catalog") / "app_files" / "products.json"
# Problem-1 Task-1: print the path itself
print(catalog_path)

# Problem-1 Task-2: print the path's name
print(catalog_path.name)
# Problem-1 Task-3: print the path's suffix
print(catalog_path.suffix)
# Problem-1 Task-4: print the path's stem
print(catalog_path.stem)
# Problem-1 Task-5: print the path's parent
print(catalog_path.parent)

# Problem-1 Task-6: print whether the path exists
print(catalog_path.exists())

Problem-2: Catalog Backup.

Write a program that builds a variable backup as a Path for catalog_backup.txt, saves the text catalog backed up to it in one step with .write_text() (end it with a newline), reads the file back in one step with .read_text(), strips the whitespace and prints it as read_text: <text>, then removes the file.

read_text: catalog backed up

from pathlib import Path

backup = Path("catalog_backup.txt")
backup.write_text("catalog backed up\n", encoding="utf-8")
print("read_text:", backup.read_text(encoding="utf-8").strip())
backup.unlink()

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Step-05: Save Next to Your Script¶

Concepts: __file__, Path(__file__).parent, .is_absolute(), mkdir(parents=True, exist_ok=True), rmdir().

Problem-1: Where Does It Land?

Write a program that builds a variable plain as a Path for orders.csv, and a variable beside_code that points at orders.csv next to THIS script (build it from __file__). Then:

• Task-1: print the folder of plain (use .parent; a bare name has none, so it prints .).
• Task-2: print the file name of beside_code (use .name).
• Task-3: print whether beside_code is pinned to one place (use .is_absolute()).

.
orders.csv
True

from pathlib import Path

plain = Path("orders.csv")
beside_code = Path(__file__).parent / "orders.csv"
# Problem-1 Task-1: the folder of a bare name
print(plain.parent)
# Problem-1 Task-2: the file name of the anchored path
print(beside_code.name)
# Problem-1 Task-3: is it pinned to one place?
print(beside_code.is_absolute())

Problem-2: A Reports Folder Beside Your Code.

Write a program that builds a variable folder pointing at a demo_orders folder next to THIS script, creates it (making any missing parents, and not failing if it is already there), writes the text id,total then jan,900 on its own line into a file orders.csv inside it, then:

• Task-1: print the folder name (use .name).
• Task-2: print whether the file is really there (use .exists()).
• Task-3: remove the file, then the folder.

demo_orders
True

from pathlib import Path

folder = Path(__file__).parent / "demo_orders"
folder.mkdir(parents=True, exist_ok=True)
report = folder / "orders.csv"
report.write_text("id,total\njan,900\n", encoding="utf-8")
# Problem-2 Task-1: the folder name
print(folder.name)
# Problem-2 Task-2: is the file really there?
print(report.exists())

# Problem-2 Task-3: remove the file, then the folder
report.unlink()
folder.rmdir()

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