Process multiple input values in Python

Question

Hi so I'm very very new to programming so please forgive me if I'm not able to ask with the correct jargon, but I'm writing a simple program for an assignment in which I'm to convert CGS units to SI units

For example:

if num == "1": #Gauss --> Tesla
        A=float(raw_input ("Enter value: "))
        print "=", A/(1e4), "T"

with this I'm only able to convert one value at a time. Is there a way I can input multiple values, perhaps separated by commas and perform the calculation on all of them simultaneously and spit out another list with the converted values?

i tried modifying the code you put to fit the rest of my program and it works, but once the values are converted, the program quits. — Christeanne
– Christeanne, Commented Apr 25, 2014 at 1:42
isn't that what you wanted? read in a comma separated list and then exit?? anyway... I've added another example on how to repeat the same procedure again and again until the user just presses enter. — Erik Kaplun
– Erik Kaplun, Commented Apr 25, 2014 at 1:43

Erik Kaplun · Accepted Answer · 2014-04-25 01:44:44Z

You can read in a comma-separated list of numbers from the user (with added whitespace possibly), then split it, strip the excessive white space, and loop over the resulting list, converting each value, putting it in a new list, and then finally outputting that list:

raw = raw_input("Enter values: ")
inputs = raw.split(",")
results = []
for i in inputs:
    num = float(i.strip())
    converted = num / 1e4
    results.append(converted)

outputs = []
for i in results:
    outputs.append(str(i))  # convert to string

print "RESULT: " + ", ".join(outputs)

Later, when you're more fluent in Python, you could make it nicer and more compact:

inputs = [float(x.strip()) for x in raw_input("Enter values: ").split(",")]
results = [x / 1e4 for x in inputs]
print "RESULT: " + ", ".join(str(x) for x in results)

or even go as far as (not recommended):

print "RESULT: " + ", ".join(str(float(x.strip()) / 1e4) for x in raw_input("Enter values: ").split(","))

If you want to keep doing that until the user enters nothing, wrap everything like this:

while True:
    raw = raw_input("Enter values: ")
    if not raw:  # user input was empty
        break
    ...  # rest of the code

Adam Smith · Accepted Answer · 2014-04-25 01:09:08Z

Sure! You'll have to provide some sort of "marker" for when you're done, though. How about this:

if num == '1':
    lst_of_nums = []
    while True: # infinite loops are good for "do this until I say not to" things
        new_num = raw_input("Enter value: ")
        if not new_num.isdigit():
            break
            # if the input is anything other than a number, break out of the loop
            # this allows for things like the empty string as well as "END" etc
        else:
            lst_of_nums.append(float(new_num))
            # otherwise, add it to the list.
    results = []
    for num in lst_of_nums:
        results.append(num/1e4)
    # this is more tersely communicated as:
    #   results = [num/1e4 for num in lst_of_nums]
    # but list comprehensions may still be beyond you.

If you're trying to enter a bunch of comma-separated values, try:

numbers_in = raw_input("Enter values, separated by commas\n>> ")
results = [float(num)/1e4 for num in numbers_in.split(',')]

Hell if you wanted to list both, construct a dictionary!

numbers_in = raw_input("Enter values, separated by commas\n>> ")
results = {float(num):float(num)/1e4 for num in numbers_in.split(',')}
for CGS,SI in results.items():
    print "%.5f = %.5fT" % (CGS, SI)
    # replaced in later versions of python with:
    #   print("{} = {}T".format(CGS,SI))

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