TypeError: 'cmp' is an invalid keyword argument for this function-Python

Question

I am new to python and i am having a script which i try to run it with Python 3.5 and i got this error

priorities[i].sort(cmp=comparer)
TypeError: 'cmp' is an invalid keyword argument for this function

Here is the function that has the error from the script

def comparer(first, second):
    """Compare function for message priorities in maintenance mode"""
    return cmp(int(first["Priority"]), int(second["Priority"]))

def get_sequence(inputs, fcm):
"""Creates right sequence for the maintenance mode"""
flags = count_flags(inputs)
sequence = []
for index, where in [(0, '"Axis"="Elevator"'), 
                     (1, '"Axis"="Aileron"'),
                     (2, '"Axis"="Rudder" or "Axis"="HS-ACE"')]:
    if len(flags[index]) == 0:
        sequence += WRITE_SEQUENCE_MAINT_0.Get(where)
    elif len(flags[index]) == 1:
        sequence += WRITE_SEQUENCE_MAINT_1.Get(where)
    elif len(flags[index]) > 1:
        sequence += WRITE_SEQUENCE_MAINT_2.Get(where)
    else:
        raise NotImplementedError("This number of flags does not make sense")

priorities = [[], [], []]
for flag in flags[0] + flags[1] + flags[2]:
    lines = WRITE_PROCESSING_MSGPRIORITY.Get('"Message Enable Flag"="%s" and "FCM Instance"="%s"' % (flag, fcm))
    if len(lines) > 0:
        priorities[{"Elevator":0, "Aileron":1, "Rudder":2}[lines[0]["Axis"]]].append(lines[0])
for i in range(3):
    priorities[i].sort(cmp=comparer)

for message in sequence:
    if "Second Highest Priority" in message["Message"]:
        new_m = priorities[{"Elevator":0, "Aileron":1, "Rudder":2}[message["Axis"]]][1]
        message["Message"] = new_m["Message"]
        message["Lane"] = new_m["Lane"]
        message["EP Bit"] = new_m["EP Bit"]
    elif "Highest Priority" in message["Message"]:
        priorities_for_rudder = priorities[{"Elev":0, "Ail":1, "Rud":2}[message["Axis"]]]
        if len(priorities_for_rudder) > 0: # This rudder message does not exist
            new_m = priorities_for_rudder[0]
            message["Message"] = new_m["Message"]
            message["Lane"] = new_m["Lane"]
            message["EP Bit"] = new_m["EP Bit"]
        else:
            message["Message"] = "Rudder Filler Message"
            message["Lane"] = "COM"
            message["EP Bit"] = "0"
return sequence

This script was written in python 2.7.

cmp was removed from sort in python 3, you have to use key instead. here is a complete explanation — Nullman
– Nullman, Commented May 28, 2019 at 12:22
Also, what is comparer? You'll have to write a function equivalent for it using key argument. — Paritosh Singh
– Paritosh Singh, Commented May 28, 2019 at 12:23

Paritosh Singh · Accepted Answer · 2019-05-28 13:38:26Z

1

There is no longer a cmp argument for sorting in python 3.

Use a key, and a function that returns a single value to be mapped for comparison.

Instead of comparer, you can use this function.

def comparer_key(item):
    """Compare keys for message priorities in maintenance mode. Returns a key."""
    return int(item["Priority"])

And then,

for i in range(3):
    priorities[i].sort(key=comparer_key)

answered May 28, 2019 at 13:38

Paritosh Singh

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