The snippet shows the use of a list of class instances to form a sortable and searchable database for solvents, or for that matter other chemicals. The list can be expanded and all the needed data added at the same time.

# a solvent database using a list of class instances
# a modification of: http://www.daniweb.com/code/snippet390.html
# EU tested with Python 2.4   10/30/2006

import operator  # for attrgetter()

class Solvent(object):
    """a structure class for solvents, self refers to the instance"""
    def __init__(self, name=9999, bp=9999, mp=9999, fp=9999, dy=9999, de=9999):
        self.name = name
        # 9999 --> not applicable
        self.bp = bp     # boiling point degC
        self.mp = mp     # melting point degC
        self.fp = fp     # flash point degC
        self.dy = dy     # density g/ml
        self.de = de     # dielectric constant


def table(solvent_list):
    """print a table of all solvent attributes"""
    title_str = "%-20s  %8s  %8s  %8s  %8s  %8s"
    data_str  = "%-20s  %8.1f  %8.1f  %8.1f  %8.3f    %8.2f"
    print "-"*72
    print title_str % ("Name", "Bp", "Mp", "Fp", "Density", "Dielectric")
    for solvent in solvent_list:
        print data_str % (solvent.name, solvent.bp, solvent.mp, solvent.fp, solvent.dy, solvent.de)
    print "-"*72
    print "9999 --> not applicable"
    print


def table_bp(solvent_list, bp_limit):
    """print a table of all solvent attributes, with bp restrictions"""
    title_str = "%-20s  %8s  %8s  %8s  %8s  %8s"
    data_str  = "%-20s  %8.1f  %8.1f  %8.1f  %8.3f    %8.2f"
    print "-"*72
    print title_str % ("Name", "Bp", "Mp", "Fp", "Density", "Dielectric")
    for solvent in solvent_list:
        if solvent.bp > bp_limit:
            print data_str % (solvent.name, solvent.bp, solvent.mp, solvent.fp, solvent.dy, solvent.de)
    print "-"*72
    print "9999 --> not applicable"
    print
    

# make a list of class Solvent instances
# also adds all the data/information
# data order = name, boiling point, melting point, flash point, density, dielectric constant
# 9999 --> not applicable
solvent_list = []
solvent_list.append(Solvent("methanol", 64.7, -97.7, 11, 0.791, 32.7))
solvent_list.append(Solvent("ethanol", 78.3, -114.1, 8, 0.789, 24.55))
solvent_list.append(Solvent("propanol iso", 82.3, -88, 22, 0.785, 19.92))
solvent_list.append(Solvent("butanol normal", 117.7, -88.6, 35, 0.81, 17.51))
solvent_list.append(Solvent("butanol secondary", 88.8, -114.7, 26, 0.805, 16.56))
solvent_list.append(Solvent("butanol tertiary", 82.2, 25.5, 4, 0.786, 10.9))
solvent_list.append(Solvent("benzyl alcohol", 205.4, -15.3, 100, 1.045, 13.1))
solvent_list.append(Solvent("acetone", 56.3, -94.7, -17, 0.791, 20.7))
solvent_list.append(Solvent("toluene", 110.6, -94.9, 4, 0.867, 2.38))
solvent_list.append(Solvent("water", 100, 0, 9999, 1, 78.5))
# got the drift, add more solvents here ...


print "Sort the solvent_list by name ..."
solvent_list.sort(key=operator.attrgetter('name'))
# ... now show a table of the solvent_list
table(solvent_list)

print

print "Sort the solvent_list by melting point ..."
solvent_list.sort(key=operator.attrgetter('mp'))
# ... now show a table of the solvent_list
table(solvent_list)

print

print "Sort the solvent_list by boiling point ..."
solvent_list.sort(key=operator.attrgetter('bp'))
# ... now show a table of the solvent_list
table(solvent_list)

print

bp_limit = 75
print "Show only solvents boiling higher than %0.1f degC:" % bp_limit
# show a boiling point restricted table
table_bp(solvent_list, bp_limit)
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