Zhaoting Chen, Steven Cunnington, Daniel Tassie, Alkistis Pourtsidou, Laura Wolz, Gabriele Autieri, Matilde Barberi-Squarotti, José Luis Bernal, Phil Bull, Stefano Camera, Isabella P. Carucci, Brandon Engelbrecht, José Fonseca, Karin Fornazier, Keith Grainge, Jiakang Han, Wenkai Hu, Melis O. Irfan, Piyanat Kittiwisit, Yichao Li, Sefa Pamuk, Mario G. Santos, Marta Spinelli, Jingying Wang, Amadeus Witzemann, Boyan Zhao

We present meer21cm, a comprehensive python package for cosmological data analysis of single-dish HI intensity mapping surveys. This package is simple to use, with a modularised code structure designed for interactive usage. meer21cm is designed for data analysis, with particular focus on the UHF-band observation of MeerKAT Large Area Synoptic Survey (MeerKLASS). We explicitly impose meer21cm to be survey-oriented, ensuring consistent modelling of observational effects in the clustering power spectrum with the survey specifications and data analysis choices. meer21cm covers a large range of data analysis procedures post calibration, including data read-in, foreground cleaning, power spectrum estimation, mock simulation, transfer function corrections and parameter inference. It handles both meer21cm intensity maps and overlapping galaxy catalogues, allowing for multi-tracer and cross-correlation analysis between MeerKLASS and optical galaxy surveys. Tested with a simulated survey of ten $750\,$deg$^2$ sky patches in the redshift sub-band $0.6\,{<}\,z\,{<}\,0.8$, the meer21cm pipeline achieves per-cent accuracy in the power spectrum estimation for $k \in [0.02, 0.2]\,{h{\rm Mpc}^{-1}}$, with deviations $\lesssim 0.5σ$ between the mock and the model power spectra, where $σ$ is the signal variance. The meer21cm package is publicly available and easy to install, with a comprehensive documentation website at https://meer21cm.readthedocs.io