Consh is an extremely simple Unix shell (like bash or csh or ksh) written in the Python language. It is almost certainly too simplistic for you to actually use as a day-to-day shell. Its only real use is learning how Unix shells work, by seeing the interaction between the fork, exec and wait system calls coded up concisely (< 100 LOC) in a friendly and easy-to-read language.
If you are after a somewhat more serious attempt at implementing a Unix shell in Python, you can check out Pysh or Pyshell, which seem to be more serious projects.
These projects also beat me to the obvious names for such a program, hence my having to settle on Consh. Consh is a deliberate misspelling of "conch", the first kind of shell with a name I could actually think of, ending in "sh" to fit in with the convention for naming shell.