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To write a Python list to a file, choose the format that suits how you will use it: write one item per line for readable text, use JSON to preserve supported list data for loading later, or use CSV for spreadsheet-style rows and columns. The examples below follow the Python 3.14.7 documentation.
Write a list to a plain-text file
For a human-readable file with one item on each line, open the file in write mode, convert each item to text, and add a newline explicitly:
items = ["apples", "bananas", "cherries"]
with open("items.txt", "w", encoding="utf-8") as file:
for item in items:
file.write(f"{item}n")file.write() writes strings, so the f-string converts each value to its text form. You can also use str(item). The with block closes the file when it exits, including when an exception occurs; Python’s tutorial recommends this practice. Use encoding="utf-8" for predictable text output unless you need another encoding. Python tutorial: reading and writing files.
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For a list of strings, writelines() is a compact alternative:
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items = ["apples", "bananas", "cherries"]
with open("items.txt", "w", encoding="utf-8") as file:
file.writelines(item + "n" for item in items)writelines() does not add line breaks by itself. Include "n" in each string when you want one item per line.
Replace a file or append to it
Opening a file with "w" creates it if needed, but replaces its existing contents if it already exists. To add items after existing content instead, open it with "a":
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with open("items.txt", "a", encoding="utf-8") as file:
for item in items:
file.write(f"{item}n")Save a list as JSON to preserve its structure
Use JSON when the list will be loaded by Python or other software that supports JSON, and you need supported values and nested structures to remain data rather than becoming plain text:
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import json
items = [1, "simple", ["nested", "list"]]
with open("items.json", "w", encoding="utf-8") as file:
json.dump(items, file, ensure_ascii=False, indent=2)
with open("items.json", encoding="utf-8") as file:
restored_items = json.load(file)json.dump() writes the list to the file, and json.load() reads it back. JSON supports built-in data types such as lists and dictionaries; arbitrary class instances need to be converted into JSON-compatible data. JSON files must use UTF-8 encoding. See the Python tutorial’s JSON section and the JSON library reference.
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A JSON file is one complete document, not a stream of separate records. Repeated calls to json.dump() on the same file do not create a valid sequence of independent JSON documents. If you need several values, put them inside one list or another enclosing structure and serialize that once; alternatively, choose a format designed for records. Python JSON library reference.
Write a list of rows to CSV
For tabular data intended for spreadsheet software or other row-and-column workflows, use Python’s csv module instead of joining values with commas yourself:
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import csv
rows = [["name", "score"], ["Ada", 98], ["Lin", 95]]
with open("scores.csv", "w", newline="", encoding="utf-8") as file:
writer = csv.writer(file)
writer.writerows(rows)Open CSV files with newline=""; the CSV module handles delimiters and quoting, including values that contain commas, quotes, or newlines. For a list of dictionaries, use csv.DictWriter, provide the field names, optionally write a header, and call writerows() for the records. See the Python CSV documentation.
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Which file format should you choose?
| Format | Best for | What it preserves |
|---|---|---|
| Plain text, one item per line | A readable list for people | Each item’s text, but not its original type or nested structure |
| JSON | Saving data to load again in Python or other JSON-capable software | Supported data types and nested structures |
| CSV | Rows and columns for spreadsheets or tabular interchange | Tabular values in CSV form, rather than a general Python list structure |
Common mistakes to avoid
- Passing a number directly to
file.write(): it expects a string. Convert values withstr(), or select JSON or CSV when you need structured output. - Expecting
writelines()to add separators: include the newline in each string if you want one item per line. - Using
"w"when you mean to keep existing contents: choose"a"to append. - Leaving text encoding implicit: specify
encoding="utf-8"for text and JSON files. - Manually joining CSV values with commas: use
csv.writerorcsv.DictWriterso values needing quotes or containing delimiters are handled correctly. - Failing to close the file: use
with open(...)so the file is closed when the block ends.
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