返回错误值

Question

I'm new to Python, learning it as part of job training, but Is started with some HTML and C/C++. Any advice into how I would make this segment work would be awesome!

def compute(tank_data): #in the parenthesis are the variables you want to pass from one def to another
aggregates = {}
list = []
for tank in tank_data: #
    sum = 0
    max_value = 0
    min_value = 1000
    #standdev = 0
    for reading in tank_data[tank]:
        sum = sum + float(reading)
        '''max_value = round(max(float(reading)),2)
        min_value = round(min(float(reading)),2)'''
        if reading >= max_value:
            max_value = float(reading)
        else:
            max_value = max_value
        if reading <= min_value:
            min_value = float(reading)
        else:
            min_value = min_value
        #standdev
    if tank in aggregates:
        aggregates[tank]['avg'] = round(sum/len(tank_data[tank]),2) #computing and printing average simutaneously
        aggregates[tank]['max'] = round(max_value,2)
        aggregates[tank]['min'] = round(min_value,2)
        #aggregates[tank]['STDEV'] = round()
    else:
        aggregates[tank] = {}
        aggregates[tank]['avg'] = round(sum/len(tank_data[tank]),2)
        aggregates[tank]['max'] = round(max_value,2)
        aggregates[tank]['min'] = round(min_value,2)
        #aggregates[tank]['STDEV'] = round()
print aggregates

I am getting correct average values for my document (checked it to excel), but only my first three max values are correct (out of 6 that I run through here), and all the min values return '1000'.

When I use the commented out section:

'''max_value = round(max(float(reading)),2)
min_value = round(min(float(reading)),2)'''

I get the error 'float' object is not iterable .

Any help would be greatly appreciated. :)

Answer 1

You have a single float/element, don't call max . if you had a list, tuple etc.. of floats you would use max on that, it makes no sense to get the max of a single number:

 round(max(map(float,tank_data[tank])),2) # iterable of floats

 round(float(reading),2)  # single float

Using your own code as I imagine this is an exercise, map all to float and just use the reading variable to check:

sm = 0 
max_value = float("-inf")
min_value = float("inf")
for reading in map(float,tank_data[tank]): # map all to float
    sm += reading
    reading = round(reading, 2) # single float
    if reading > max_value:
        max_value = reading
    if reading < min_value:
        min_value = reading

You don't need to use max_value = round(... you are doing the logic with your if/else blocks. You should only update after you have checked the current values against the lowest/highest seen so far.

You should also avoid using sum and list as variable names as you are shadowing the builtin functions.

Answer 2

Use the built-in functions of python:

def compute(tank_data):
    aggregates = {}
    list = []
    for tank, data in tank_data.iteritems():
        numbers = [float(v) for v in data]
        total = sum(numbers)
        max_value = max(numbers)
        min_value = min(numbers)
        info = {
            'avg': round(total/len(numbers),2) 
            'max': round(max_value,2),
            'min': round(min_value,2),
        }
        aggregates.set_default(tank, {}).update(info)
    print aggregates