segno: A Pure Python QR Encoder That Also Writes SVG, EPS and PDF

A standard conform encoder with no dependencies

segno implements the ISO/IEC 18004:2015(E) QR Code bar code symbology specification and produces QR Codes and Micro QR Codes. The package is pure Python with no dependencies, and the dependency list in the package metadata reflects that: the single entry is `importlib-metadata>=3.6.0` guarded by a `python_version < '3.10'` marker, which exists only to read package metadata on older interpreters. Everything else is standard library, which is what makes it droppable into a service or a build script without a wheel to vendor. The project claims more than 1500 test cases with coverage at or above 98 percent to verify standard conform generation, and the package is classified as Development Status 5 - Production/Stable with a BSD licence.

The output format list is unusually long

The serialization formats are the reason many people pick this library. Segno provides Scalable Vector Graphics, Encapsulated PostScript, Portable Network Graphics, Portable Document Format, the Netpbm family of PAM, PBM and PPM, LaTeX in the form of PGF and TikZ, X PixMap and X Bitmap. None of these serializers require an external library, which means a vector PDF can be produced on a machine with nothing installed but Python. The vector formats matter for print and for large-format output, where a raster PNG scales badly, and the presence of PGF and TikZ means a code can be placed directly in a LaTeX document. The name comes from the Italian for sign or symbol, and the project is the work of Lars Heuer.

Micro QR codes appear without being asked for

The default behaviour catches people out. If the content is small enough, segno generates a Micro QR code, which is a smaller symbol with fewer modules and a more limited character set.

>>> import segno
>>> qrcode = segno.make('RAIN')
>>> qrcode.is_micro
True
>>> qrcode.designator
'M2-M'

A Micro QR is denser but supports less, so a reader that only handles full QR codes will not read it. If that is not what you want, pass `micro=False` and you get a standard code instead.

>>> import segno
>>> qrcode = segno.make('RAIN', micro=False)
>>> qrcode.is_micro
False
>>> qrcode.designator
'1-H'

There are also explicit factory functions. `segno.make_qr()` always produces a full QR code and `segno.make_micro()` always produces a Micro QR code, raising an error when the data is too large for one.

>>> micro_qrcode = segno.make_micro('Nick Cave and the Bad Seeds')
Traceback (most recent call last):
    ...
DataOverflowError: Data too large. No Micro QR Code can handle the provided data

Saving a code with scaling and colour options

The save call takes the output options, and the same object can be written in several formats. A minimal call writes a PNG.

import segno
qrcode = segno.make('Yellow Submarine')
qrcode.save('yellow-submarine.png')

Scaling, colour and background are parameters on the same method, so a scaled transparent PNG and a dark-blue SVG differ only in the arguments.

>>> qrcode.save('up-jumped-the-devil-2.png', scale=10)
>>> qrcode.save('up-jumped-the-devil-3.png', light=None)
>>> qrcode.save('up-jumped-the-devil.pdf', scale=10)
>>> qrcode.save('up-jumped-the-devil.svg', scale=10, dark='darkblue')

The `light=None` argument is the one to remember, since it produces transparent light modules rather than white ones. The designator attribute is worth knowing too, because it returns the version and the error correction level in one string, and it tells you what the encoder actually chose: the documented example picks a minimal version with an optimal error level without changing that version, returning `2-Q`.

The command line prints a code to your terminal

There is a console script, registered in the package metadata as the console script `segno`, pointing at `segno.cli:main`, and the simplest invocation prints a QR code to the terminal.

segno "Comfortably Numb"

The output argument writes a file instead, and the same flags cover scale, colours and border.

segno -o=raincoat.svg "Famous Blue Raincoat"
segno --scale 10 --dark darkblue --border 0 --output=fire.svg "Who by Fire"
segno --scale 10 --light transparent --output=miracle.png "Waiting for the Miracle"

The `--border 0` flag removes the quiet zone, the blank margin around the symbol that scanners rely on, so it is worth setting only when you already control the surrounding layout and want the code flush with other elements.

Installing it from PyPI, conda or a distro package

Installation is one command from PyPI.

pip install segno

It is also on conda-forge.

conda install -c conda-forge segno

And Debian ships it under the name python3-segno.

apt-get install python3-segno

Arch Linux has a package as well, called python-segno.

pacman -S python-segno

The presence of distribution packages is a practical point for anyone running this in a locked-down environment, where pip may not be an option. The package metadata also pins the minimum interpreter at Python 3.5 and marks the project as Python 3 only.

Beyond plain codes: contact data, EPC, WIFI and structured append

Segno ships high level factories for the payloads people actually need to encode, including contact data in vCard and MeCard form, EPC QR Codes, and WIFI QR Codes carrying a network configuration. On top of that sits Structured Append mode, which splits a message across several QR codes and is the mechanism behind multi-part codes that a scanner reassembles. The main modes it supports are listed in the feature list along with Hanzi mode, which is the Chinese character mode of the specification. Two of the features are extensions rather than core: colourful QR codes, where the data is spread across module colours and which also work with Micro QR codes, and artistic QR codes, which require the separate qrcode-artistic plug-in and can even produce animated codes. Of these, only the artistic codes need the plug-in.

How it is built and packaged

The build uses flit_core as the build backend, and the version is dynamic, read from the source rather than duplicated in the metadata. The repository root shows a documentation directory, a `tests/` directory, a `sandbox/` directory and a `data/` directory, and the packaging configuration treats `data/` as external data for flit. Coverage is configured with branch coverage enabled. The source distribution explicitly includes the docs, the tests, the licence, the reStructuredText files, the noxfile and the manifest, and excludes the GitHub directory and the sandbox. A noxfile at the root is the usual sign that the test and lint sessions are managed with nox rather than a bespoke script. The examples directory covers Django, Flask, a logo case and plain text output, and the licence is BSD-3-Clause.

Editorial conclusion

segno fits a Python project that needs a conformant QR code without adding a binary dependency, and it is the safer choice when the output has to be vector, since SVG, EPS and PDF writers come with no external library behind them. It is the wrong choice if you want colourful or animated artistic codes, since those need the separate qrcode-artistic plug-in, and it supports structured append, splitting a message across several QR codes, if that is what you need. Before adopting it, check the micro behaviour, because segno.make returns a Micro QR code automatically when the content is short enough.

Frequently asked questions

Official sources

1. heuer/segno on GitHub
2. License: BSD-3-Clause
3. Project website
4. README
5. Releases