Python: TypeError: can't multiply sequence by non-int of type 'float' when using float parameters

Question

I'm writing a program to calculate left-hand, right-hand, and mid-point Riemann Sums (I misspelled it everywhere else). I decided to use python (I have some experience with it) to write the script and eventually build up a library of math tools that I could quickly execute using bash aliases and scripts. However, I'm running into problems with my script. Because I need to evaluate a function, I used this library. After writing the script, I tried to execute it using the following command:

python -c "from reimann import reimann; print(reimann(1.0,2.718281828459045,10,'1/x','midpoint'))"

This should return about 1, and it does when run from the script, but I get the following error when run as shown above:

Traceback (most recent call last):
File "<string>", line 1, in <module>
File "reimann.py", line 3, in reimann
delta_x = ((float(interval_b) - float(interval_a))/float(num_intervals * 1.0))
TypeError: can't multiply sequence by non-int of type 'float'

even when run with the following command:

python -c "from reimann import reimann; print(reimann(float(1.0),float(2.718281828459045),10.0,'1/x','midpoint'))"

Any help is greatly appreciated! Below is my code:

from simpleeval import simple_eval
def reimann (equation, interval_a, interval_b, num_intervals, type_sum):
    delta_x = ((float(interval_b) - float(interval_a))/float(num_intervals * 1.0))
    ans = 0;
    if type_sum == "left":
            x = interval_a
            while x < (interval_b - delta_x):
                    ans += simple_eval(equation, names={"x": x})
                    x += delta_x
    else:
            if type_sum == "right":
                    x = interval_a + delta_x
                    while x < interval_b:
                            ans += simple_eval(equation, names={"x": x})
                            x += delta_x
            else:
                    if type_sum == "midpoint":
                            x = interval_a 
                            while x < (interval_b - delta_x):
                                    ans += simple_eval(equation, names={"x": x})
                                    x += delta_x

                            x = interval_a + delta_x
                            while x < interval_b:
                                    ans += simple_eval(equation, names={"x": x})
                                    x += delta_x
                            ans /= 2
    ans *= delta_x
    return ans

#print(reimann("1/x", 1, 2.718281828459045, 10000, "midpoint") This works correctly

NOTE: I put the parameters in wrong, I'm sorry for wasting everyones' time. Thanks for the help.

Apparently it is not. Please include the output of `type(num_intervals)`. I suspect it is an integer-like string. — DYZ, Mar 17 '18 at 18:05
What did you expect `'1/x'` to do? You are trying to multiply that string with a float, and that doesn't work (but multiplication with an integer would, repeating the string). — Martijn Pieters, Mar 17 '18 at 18:13

score 1 · Answer 1 · answered Mar 17 '18 at 18:06

1

In your line python -c "from reimann import reimann; print(reimann(float(1.0),float(2.718281828459045),10.0,'1/x','midpoint'))", you're passing a string ('1/x') as num_intervals.

If I understand your code correctly, it should be python -c "from reimann import reimann; print(reimann('1/x', float(1.0),float(2.718281828459045),10.0,'midpoint'))"

answered Mar 17 '18 at 18:06

Trap

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3
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Yep. You're completely right. I'm sorry for wasting everyone's time with my myopic ways. Thanks so much for the help though. – Alex Jackson Mar 17 '18 at 18:25

Python: TypeError: can't multiply sequence by non-int of type 'float' when using float parameters

1 Answers1