mutable-print

Edit printed terminal text after it's already been printed.

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What is mutable-print?

Once you call print(), that line is done — you can't touch it. If you want to show a progress bar, a live status, or just update a value in place, you're stuck reprinting the same line over and over, which looks messy.

mutable-print fixes that. It gives you a handle to any line you've printed, so you can update, replace, append, clear, or transform it at any point — even after printing more lines below it.

pip install mutable-print

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Your first mutable line

from mutable_print import mutable_print

line = mutable_print("Loading...", flush=True)
# ... do some work ...
line("Done!")

mutable_print works exactly like Python's built-in print, except it returns an object you can use to edit the line later. Calling that object like a function replaces the content.

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Updating content

Calling the object directly

The simplest way to update a line — just call it like a function with new content.

line("Processing 3/10...")
line("Processing 7/10...")
line("All done!")

You can also change sep and end at the same time. If you leave them out, the current values are kept.

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line.set(*text)

Replace the entire content with something new. Equivalent to calling the object directly, but chainable.

line.set("New content here")

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line.replace(old, new, count=-1)

Replace occurrences of a substring inside the current content. By default replaces all of them — pass count to limit it.

line.replace("FAILED", "OK")
line.replace("x", "✓", 1)  # only the first one

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line.regex_replace(pattern, replacement, flags=0)

Same idea as replace, but with a regex pattern. Supports backreferences and all standard re flags.

line.regex_replace(r"\d+", "??")
line.regex_replace(r"(\w+) error", r"\1 warning", flags=re.IGNORECASE)

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Adding content

line.append(*text)

Adds text to the end of the current content.

line.append(" ✓")

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line.prepend(*text)

Adds text to the beginning of the current content.

line.prepend("[INFO] ")

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Other operations

line.upper() / line.lower()

Converts the current content to uppercase or lowercase.

line.upper()  # "hello world" → "HELLO WORLD"

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line.clear()

Wipes the content entirely — sets it to an empty string.

line.clear()

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line.get()

Returns the current content as a string, without printing anything.

status = line.get()

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Chaining

All methods except get() return the mutable_print instance, so you can chain operations together.

line.prepend("[WARN] ").replace("timeout", "slow response").upper()

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Full API reference

mutable_print(*args, sep=" ", end="\n", file=None, flush=False)

Creates the mutable print object and immediately prints the initial content.

Parameter	Type	Default	Description
*args	Any	—	Values to print
sep	str	" "	Separator between values
end	str	"\n"	String appended at the end
file	TextIO	sys.stdout	Output stream
flush	bool	False	Whether to flush immediately

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Method summary

Method	What it does
line(...)	Replace content and reprint
line.set(*text)	Replace content (chainable)
line.replace(old, new, count=-1)	Substring replacement
line.regex_replace(pattern, repl, flags=0)	Regex replacement
line.append(*text)	Add to the end
line.prepend(*text)	Add to the beginning
line.upper()	Uppercase
line.lower()	Lowercase
line.clear()	Wipe content
line.get()	Return content as string

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How it works

Internally, mutable-print keeps a global list of everything that's been printed. When you update a line, it calculates how many lines up that content lives, moves the cursor back using ANSI escape codes (\033[A), clears from there, and reprints everything from that point downward.

This is what makes retroactive edits work correctly — even if you've printed ten more lines after the one you're editing, the update lands in the right place and the rest of the output follows cleanly.

Uses only standard Python modules: sys, re, and typing.