My college textbook which introduced me to the constitutions of several countries.A textbook that was actually good fun.
Pakistan's 1973 constitution,still operative after several suspensions and amendments.It takes elements from other constitutions,mixes them with local provisions and is a fairly unwieldy document.I didn't find its study all that appealing.But it has endured somehow,its predecessors from 1956 and 1962 didn't.
The unwritten British constitution,which I found interesting precisely because it is unwritten. Useless institutions like the House of Lords and and especially The Monarchy,which I later found has great entertainment value despite its uselessness.
The U.S. constitution,noteworthy for its brevity, its sheer rigidity and the checks and balances which can seriously hobble government.The US still persists with the Electoral College,which can create farcical situations like the 2000 election. I continue to enjoy the political circus in the US,though it becomes tiresome in the election year.
The Soviet Constitution,which I don't remember much about except its authoritarianism and institutions like the Presidium and Politbureau.
The Swiss constitution,which notably allows a rotating Presidency and Vice Presidency.Fascinating,no single individual is allowed to dominate.