The Tool Desk
Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →To keep a Python variable after a program exits, write its value to a file and load it in the next run. For ordinary lists and dictionaries, JSON is a readable, portable default: use json.dump() to save and json.load() to restore. For a single text value, basic file I/O may be enough.
Save and load a dictionary with JSON
JSON works well for common Python data such as dictionaries, lists, strings, numbers, booleans and nested combinations of them. It stores text, so open the file in text mode and specify an encoding.
import json
settings = {"theme": "dark", "volume": 7}
with open("settings.json", "w", encoding="utf-8") as file:
json.dump(settings, file, indent=2)
with open("settings.json", "r", encoding="utf-8") as file:
settings = json.load(file)
print(settings)The write step creates or replaces settings.json in the program’s current working directory. The read step parses that file back into a Python value, so settings is a dictionary again. The with blocks close the files automatically.
Use "w" when you intend to replace the saved contents. If you need to preserve prior file contents, choose a format and update strategy that matches the data rather than assuming another json.dump() call will merge dictionaries.
Recommended Free Tools
#1 Best Overall
Save one text value with ordinary file I/O
For a simple string, the built-in file methods are sufficient:
name = "Ada"
with open("name.txt", "w", encoding="utf-8") as file:
file.write(name)
with open("name.txt", "r", encoding="utf-8") as file:
name = file.read()read() returns text. If you save a number this way, convert the text back when loading it—for example, use int() for an integer or float() for a floating-point value. JSON handles common primitive types and their conversions for you.
Choose a storage method for the data
| Need | Starting point | Trade-off |
|---|---|---|
| Plain text or one small primitive value | Text file I/O | You must parse or convert values such as numbers when reading them. |
| Lists, dictionaries, settings or portable structured data | JSON | Human-readable and interoperable, but custom objects need explicit conversion. |
| A richer Python object graph, with both ends controlled and trusted | pickle |
Python-specific and binary; loading untrusted data is unsafe. |
| A persistent mapping accessed by keys | shelve |
Provides a persistence interface backed by DBM-style storage; check its documented restrictions. |
| Relational data or database-style queries | sqlite3 |
More structure than saving one serialized object; use it when the data or access pattern calls for a database. |
When to use pickle—and its security boundary
pickle can serialize a broader range of Python objects than JSON, but the resulting files are Python-specific and use binary mode:
import pickle
with open("state.pkl", "wb") as file:
pickle.dump(state, file)
with open("state.pkl", "rb") as file:
state = pickle.load(file)Python’s documentation warns: “Only unpickle data you trust.” Unpickling a malicious file can execute code. Use pickle only when you control and trust the file and the source that produced it; do not load a file received from an unknown person or downloaded from an untrusted source.
What JSON cannot save directly
JSON does not directly encode every Python type or arbitrary class instance. For unsupported values, convert them into JSON-supported structures—such as dictionaries, lists and primitive values—and write corresponding code to reconstruct the original form after loading.
For a dictionary that needs to survive closing and rerunning a program, the key idea is to persist its value explicitly: load the saved data when the program starts, change the dictionary, then write the updated value back when needed. A Python variable in memory does not persist merely because the program used it.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
