I am building a program in python. I have two lists and I want to loop through each of them to see if the elements are equal if they are I want to remove the one element from the list and I want to run a few codes. When this is done I want to return back to the loop to compare the lists again. until one list is empty and the program will continue.
I tried this but just can not get my mind to unblock it! Thank you.
x = [1,2,3,4,5,6,7]
y = [28,1,2,3,4,5,6]
for i in x:
for a in y:
while i == a:
x.remove(i)
How do I tell python to return to the first loop??
Use flag approch
x = [1,2,3,4,5,6,7]
y = [28,1,2,3,4,5,6]
flag=False
for i in x:
flag=False
for a in y:
while i == a:
x.remove(i)
flag=True
if(flag==True):
break
Related
I'm struggling to grasp the problem here. I already tried everything but the issue persist.
Basically I have a list of random numbers and when I try to compare the vaalues inside loop it throws "IndexError: list index out of range"
I even tried with range(len(who) and len(who) . Same thing. When put 0 instead "currentskill" which is int variable it works. What I don't understand is why comparing both values throws this Error. It just doesn't make sence...
Am I not comparing a value but the index itself ???
EDIT: I even tried with print(i) / print(who[i] to see if everything is clean and where it stops, and I'm definitelly not going outside of index
who = [2, 0, 1]
currentskill = 1
for i in who:
if who[i] == currentskill: # IndexError: list index out of range
who.pop(i)
The problem is once you start popping out elements list size varies
For eg take a list of size 6
But you iterate over all indices up to len(l)-1 = 6-1 = 5 and the index 5 does not exist in the list after removing elements in a previous iteration.
solution for this problem,
l = [x for x in l if x]
Here x is a condition you want to implement on the element of the list which you are iterating.
As stated by #Hemesh
The problem is once you start popping out elements list size varies
Problem solved. I'm just popping the element outside the loop now and it works:
def deleteskill(who, currentskill):
temp = 0
for i in range(len(who)):
if who[i] == currentskill:
temp = i
who.pop(temp)
There are two problems in your code:
mixing up the values and indexes, as pointed out by another answer; and
modifying the list while iterating over it
The solution depends on whether you want to remove just one item, or potentially multiple.
For removing just one item:
for idx, i in enumerate(who)::
if i == currentskill:
who.pop(idx)
break
For removing multiple items:
to_remove = []
for idx, i in enumerate(who)::
if i == currentskill:
to_remove.append[idx]
for idx in reversed(to_remove):
who.pop(idx)
Depending on the situation, it may be easier to create a new list instead:
who = [i for i in who if i != currentskill]
Your logic is wrong. To get the index as well as the value, use the built-in function enumerate:
idx_to_remove = []
for idx, i in enumerate(who)::
if i == currentskill:
idx_to_remove.append[idx]
for idx in reversed(idx_to_remove):
who.pop(idx)
Edited after suggestion from #sabik
The task is:
User enters a number, you take 1 number from the left, one from the right and sum it. Then you take the rest of this number and sum every digit in it. then you get two answers. You have to sort them from biggest to lowest and make them into a one solid number. I solved it, but i don't like how it looks like. i mean the task is pretty simple but my code looks like trash. Maybe i should use some more built-in functions and libraries. If so, could you please advise me some? Thank you
a = int(input())
b = [int(i) for i in str(a)]
closesum = 0
d = []
e = ""
farsum = b[0] + b[-1]
print(farsum)
b.pop(0)
b.pop(-1)
print(b)
for i in b:
closesum += i
print(closesum)
d.append(int(closesum))
d.append(int(farsum))
print(d)
for i in sorted(d, reverse = True):
e += str(i)
print(int(e))
input()
You can use reduce
from functools import reduce
a = [0,1,2,3,4,5,6,7,8,9]
print(reduce(lambda x, y: x + y, a))
# 45
and you can just pass in a shortened list instead of poping elements: b[1:-1]
The first two lines:
str_input = input() # input will always read strings
num_list = [int(i) for i in str_input]
the for loop at the end is useless and there is no need to sort only 2 elements. You can just use a simple if..else condition to print what you want.
You don't need a loop to sum a slice of a list. You can also use join to concatenate a list of strings without looping. This implementation converts to string before sorting (the result would be the same). You could convert to string after sorting using map(str,...)
farsum = b[0] + b[-1]
closesum = sum(b[1:-2])
"".join(sorted((str(farsum),str(closesum)),reverse=True))
I am very new in Python, and I am really surprised at the following line of code.
p, q = [int(x) for x in input().split()]
how to write basic??
You can make a loop instead to understand better, but the code won't work because the logic is false:
your_input = input().split()
list_ = []
for x in your_input:
list_.append(int(x))
p, q = list_
The .split() put the str in input in a list so you just have one element and one loop. But the p,q = at the end suggests it waits two elements in the list. So it can't work. Maybe you can delete the .split() if you want each digit of a number less than 100. Depends on the result you want.
The function must return a list consisting of the numbers greater than the second number in the function
It must be able to do the following when functioning:
returnGreater([1,2,3,4,5], 3)
[4,5]
returnGreater([-8,2,-4,1,3,-5],3)
[]
Here's what I have (I've gone through a few iterations), though I get a Type Error for trying to use a ">" symbol between an int and list:
def returnGreater (x,y):
"x:list(int) , return:list(int)"
#greater: int
greater = []
for y in x:
#x: int
if x > y:
x = greater
return greater
You're using the name y for two different things in your code. It's both an argument (the number to compare against) and the loop variable. You should use a different name for one of those.
I'd strongly suggest picking meaningful names, as that will make it much clearer what each variable means, as well as making it much less likely you'll use the same name for two different things. For instance, here's how I'd name the variables (getting rid of both x and y):
def returnGreater(list_of_numbers, threshold):
greater = []
for item in list_of_numbers:
if item > threshold:
greater.append(item)
return greater
You had another issue with the line x = greater, which didn't do anything useful (it replaced the reference to the original list with a reference to the empty greater list. You should be appending the item you just compared to the greater list instead.
I recommend filter. Easy and Graceful way.
def returnGreater(x, y):
return list(filter(lambda a:a>y, x))
It means, filter each element a in list x using lambda whether a is greater than y or not.
List Comprehensions
def returnGreater(_list, value):
return [x for x in _list if x > value]
You know when you find a solution via trial and error but you stumbled so much thtat you can't understand the answer now?
Well this is happening to me with this piece:
entr = [list(int(x) for x in input().split()) for i in range(int(input()))]
The input is done by copying and pasting this whole block:
9
8327 0
0070 0
2681 2
1767 0
3976 0
9214 2
2271 2
4633 0
9500 1
What is my list comprehension exactly doing in each step? And taking into account this: How can I rewrite it using for loops?
In fact, your code is not a nested list-comprehension, beause you use list construtor rather than mere list-comprehension.
This line serves as same as your code:
entr = [[int(x) for x in input().split()] for i in range(int(input()))]
To understand this line, you must remember the basic structure of list-comprehension in python, it consists of two component obj and condition with a square brackets surrounding:
lst = [obj condition]
it can be converted to a loop like this:
lst = []
condition:
lst.append(obj)
So, back to this question.
What you need to do now is to break the nested list-comprehension into loop in loop, usually you begin from the condition in latter part, from outer space to inner space. You got:
entr = []
for i in range(int(input())):
entr.append([int(x) for x in input().split()])) # the obj is a list in this case.
And now, you can break the list-comprehension in line 3.
entr = []
for i in range(int(input())):
entry = []
for x in input().split():
entry.append(int(x))
entr.append(entry)
So, now the stuff the original line can be easily understand.
the program construct a entry list named entr;
the program ask for user input and convert the input string into an int, which is the number of the entrys you want to input(assume it is num);
the program ask for user input for num times, each time you should input something seperate with spaces.
The program split every string into a list (named entry in above code) you input with str.split() method (with parameter sep default to space). And append each entry list in every loop.
for every element in the entry list, it converted to int.
My English may be poor, feel free to improve my answer:)
That is equivalent to this:
entr = []
for i in range(int(input())):
row = []
for x in input().split():
row.append(int(x))
entr.append(row)
You can copy-paste that into a list comprehension in a couple steps. First the inner loop/list:
entr = []
for i in range(int(input())):
row = [int(x) for x in input().split()]
entr.append(row)
Without the row variable:
entr = []
for i in range(int(input())):
entr.append([int(x) for x in input().split()])
Then the outer loop/list (copied over multiple lines for clarity):
entr = [
[int(x) for x in input().split()]
for i in range(int(input()))
]
You have that same nested comprehension except that the inner one has been written as a generator passed to the list constructor so it looks like list(int(x) for x in input().split()) instead of [int(x) for x in input().split()]. That's a little more confusing than using a list comprehension.
I hope that explanation helps!