Conservative Constraints on Early Cosmology: an illustration of the
  Monte Python cosmological parameter inference code
  Models for the latest stages of the cosmological evolution rely on a less
solid theoretical and observational ground than the description of earlier
stages like BBN and recombination. As suggested in a previous work by
Vonlanthen et al., it is possible to tweak the analysis of CMB data in such way
to avoid making assumptions on the late evolution, and obtain robust
constraints on "early cosmology parameters". We extend this method in order to
marginalise the results over CMB lensing contamination, and present updated
results based on recent CMB data. Our constraints on the minimal early
cosmology model are weaker than in a standard LCDM analysis, but do not
conflict with this model. Besides, we obtain conservative bounds on the
effective neutrino number and neutrino mass, showing no hints for extra
relativistic degrees of freedom, and proving in a robust way that neutrinos
experienced their non-relativistic transition after the time of photon
decoupling. This analysis is also an occasion to describe the main features of
the new parameter inference code Monte Python, that we release together with
this paper. Monte Python is a user-friendly alternative to other public codes
like CosmoMC, interfaced with the Boltzmann code class.
