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I just want to use the for loop for the t variable in my function:
l = []
def func(s):
for i in range(1, 100):
t = i
p = t * 2 + s * 2
return p
l.append(func(10))
print l
I want the value of t to go from 1 to 99 and and print a list of all the value, but I always end up getting l = [218].
485
Yes, I can declare multiple variables in a for-loop. And you, too, can now declare multiple variables, in a for-loop, as follows: Just separate the multiple variables in the initialization statement with commas. Do not forget to end the complete initialization statement with a semicolon.
The use of multiple variables in a for loop in Python can be applied to lists or dictionaries, but it does not work for a general error. These multiple assignments of variables simultaneously, in the same line of code, are known as iterable unpacking.
With two arguments in the range function, the sequence starts at the first value and ends one before the second argument. Programmers use x or i as a stepper variable.
How can I include two variables in the same for loop? t1 = [a list of integers, strings and lists] t2 = [another list of integers, strings and lists] def f(t): #a function that will read lists "t1" and "t2" and return all elements that are identical for i in range(len(t1)) and for j in range(len(t2)): ...
I assume you have NumPy installed (at least your original question suggested it), so I'll present a way how you can get your result using numpy-arrays in a very efficient manner (without any list-comprehensions and explicit iterations):
> import numpy as np
> s = 10
> l = np.arange(1, 100) * 2 + s * 2 # Arrange produces an array. Syntax is like "range".
> print(l)
array([ 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46,
48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72,
74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98,
100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124,
126, 128, 130, 132, 134, 136, 138, 140, 142, 144, 146, 148, 150,
152, 154, 156, 158, 160, 162, 164, 166, 168, 170, 172, 174, 176,
178, 180, 182, 184, 186, 188, 190, 192, 194, 196, 198, 200, 202,
204, 206, 208, 210, 212, 214, 216, 218])
I used the fact that mathematical operations on NumPy arrays affect all elements. Therefore it is so easy to write the operation: np.arange(1, 100) * 2, because it multiplies every element with 2 and numpy.arange is a possibility to create an array containing all the numbers between a given start and stop with an optional step (just like the python range).
With NumPy it wouldn't be a good choice to append single values (because this recreates the whole array and not just appends values). In most cases it's best to create an array with the final size and shape and operate directly on it. Of course you can concatenate or append different NumPy arrays, but as mentioned it always creates a completely new array and is therefore not very efficient (if used regularly).
So now a few observations on your initial attempt and why it didn't work: Your function created lots of numbers, but it overrides them in each loop and only returns the last one:
def func(s):
for i in range(1, 100):
t = i
p = t * 2 + s * 2
# Next iteration of the loop just overwrites p
# Returns only the last p
return p
You could make this a generator (with yield instead of return), but that's probably overkill here, I'll show it nevertheless :-)
l = []
def func(s):
for i in range(1, 100):
p = i * 2 + s * 2
yield p
l.append(list(func(10))) # Need to convert the generator to a list here.
# In this case a simple "l = list(func(10))" would be easier if you don't need to append.
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