primer3-py

2.3.0 verified Fri May 01 auth: no python

Python bindings for the Primer3 primer design and analysis library. Current version 2.3.0 supports Python 3.8–3.14. Actively maintained, with occasional releases.

pip install primer3-py

Common errors

error AttributeError: module 'primer3' has no attribute 'setGlobals' ↓

cause setGlobals was removed in v1.0.0.

fix

Use primer3.set_global_flags(parameters) instead.

error TypeError: calc_tm() got an unexpected keyword argument 'mv_conc' ↓

cause calc_tm uses keyword arguments for salt and divalent concentrations; incorrect param name.

fix

Use valid keyword arguments: mv_conc, dv_conc, dntp_conc, dna_conc.

error ValueError: Sequence 'XYZ' contains invalid characters ↓

cause Sequence contains non-DNA letters or whitespace.

fix

Clean sequence with primer3.clean_sequence(seq) or validate manually.

Warnings

breaking In v2.0.0, the output dictionary keys changed: list versions of PRIMER_PAIR, PRIMER_LEFT, PRIMER_RIGHT, PRIMER_INTERNAL were added. Code relying on old key shapes may break if not adapted. ↓

fix Use both old and new keys or update code to use list versions.

breaking In v1.0.0, setGlobals was removed; use primer3.set_global_flags or direct parameter passing instead. ↓

fix Replace primer3.setGlobals(...) with primer3.set_global_flags(...) or pass parameters as dict.

gotcha calc_tm accepts sequences with ambiguous bases (e.g., 'N') but may raise exceptions for invalid characters. Ensure input is valid DNA. ↓

fix Validate or sanitize sequences before passing to calc_tm.

Imports

bindings
wrong
```
from primer3 import *
```
correct
```
import primer3
```
Wildcard imports discouraged; use explicit import.

Quickstart

Calculate Tm of a DNA sequence.

import primer3

seq = 'AGCAGCGCGTATACGCGTATATACGCGATATCGCGTAGCT'
result = primer3.calc_tm(seq)
print(result)