[book] Improve PostgreSQL configuration section
* Do not advice for specific PostgreSQL version (point to meta-packages if
available in Linux distros);
* First mention packages from Linux distros, put the link to official postgres
documentation at the end;
Closes #2725302.
try:
rtype, = __args__
except ValueError:
print 'USAGE: cubicweb-ctl shell <instance> detect_cycle.py -- <relation type>'
print
graph = {}
for fromeid, toeid in rql('Any X,Y WHERE X %s Y' % rtype):
graph.setdefault(fromeid, []).append(toeid)
from logilab.common.graph import get_cycles
for cycle in get_cycles(graph):
print 'cycle', '->'.join(str(n) for n in cycle)