Workshop: Files, JSON, and Paths (Optional, Self-Study)¶

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Five optional workshop problems, one per concept step, in a car scenario. Each one that creates a file tidies up with .unlink(). Self-study: check python-workshop/solutions.

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

Concepts: with open(), "w", "r", .unlink().

Write a program that writes the two log lines Engine started and Drove 50 km to car_log.txt, reads the whole file back as one string and prints it, then removes the file.

Engine started
Drove 50 km

from pathlib import Path

with open("car_log.txt", "w", encoding="utf-8") as f:
    f.write("Engine started\n")
    f.write("Drove 50 km\n")
with open("car_log.txt", "r", encoding="utf-8") as f:
    print(f.read())
Path("car_log.txt").unlink()

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

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

Write a program that writes Oil change to service.txt, then appends Tyre rotation to the same file, then reads the file line by line and prints each line as service: <text> (strip the newline).

service: Oil change
service: Tyre rotation

from pathlib import Path

with open("service.txt", "w", encoding="utf-8") as f:
    f.write("Oil change\n")
with open("service.txt", "a", encoding="utf-8") as f:
    f.write("Tyre rotation\n")
with open("service.txt", "r", encoding="utf-8") as f:
    for line in f:
        print("service:", line.strip())
Path("service.txt").unlink()

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

Concepts: json.dump, json.load.

Write a program that saves the dict {"brand": "Mazda", "year": 2020} to car.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 brand value.

{'brand': 'Mazda', 'year': 2020}
Mazda

import json
from pathlib import Path

car = {"brand": "Mazda", "year": 2020}
with open("car.json", "w", encoding="utf-8") as f:
    json.dump(car, f)
with open("car.json", "r", encoding="utf-8") as f:
    loaded = json.load(f)
# Task-1: print the whole loaded dict
print(loaded)
# Task-2: print the brand value
print(loaded["brand"])
Path("car.json").unlink()

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Step-04: Paths with pathlib¶

Concepts: Path join with /, .name/.suffix/.parent, .exists().

Write a program that builds a variable p by joining the parts garage, cars, and mazda.txt 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 parent (use .parent).
• Task-5: print whether the path exists (use .exists(); this path was never created, so it is False).

garage/cars/mazda.txt
mazda.txt
.txt
garage/cars
False

from pathlib import Path

p = Path("garage") / "cars" / "mazda.txt"
# Task-1: print the path itself
print(p)
# Task-2: print the path's name
print(p.name)
# Task-3: print the path's suffix
print(p.suffix)
# Task-4: print the path's parent
print(p.parent)
# Task-5: print whether the path exists
print(p.exists())

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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 the Service Log Land?

Write a program that builds a variable plain as a Path for service.log, and a variable beside_code that points at service.log 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()).

.
service.log
True

from pathlib import Path

plain = Path("service.log")
beside_code = Path(__file__).parent / "service.log"
# 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 Garage Records Folder Beside Your Code.

Write a program that builds a variable folder pointing at a demo_garage folder next to THIS script, creates it (making any missing parents, and not failing if it is already there), writes the text car,km then mazda,42000 on its own line into a file service.log 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_garage
True

from pathlib import Path

folder = Path(__file__).parent / "demo_garage"
folder.mkdir(parents=True, exist_ok=True)
log = folder / "service.log"
log.write_text("car,km\nmazda,42000\n", encoding="utf-8")
# Problem-2 Task-1: the folder name
print(folder.name)
# Problem-2 Task-2: is the file really there?
print(log.exists())

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

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Workshop: Error Handling and Debugging Next: Workshop: Standard Library Essentials