I have been studying about the list comprehension. So I have decided to code something with a for loop which looks like
babe = 122132323
b = [n for n in babe]
print b
When I run the above code it gives me error like TypeError: 'int' object is not iterable
I have researched about these similar errors but I don't know what wrong with my code. It would be really appreciated if anyone tell me how can I overcome this error and make the code work.
int variables are not sequences and neither iterable. you have to make it string.
In [60]: babe = '122132323'
In [61]: b = [n for n in babe] #this pick every item from left and store it in `n` then return n.
In [62]: b
Out[62]: ['1', '2', '2', '1', '3', '2', '3', '2', '3']
or simple use list builtin-function.
[63]: list(babe)
Out[63]: ['1', '2', '2', '1', '3', '2', '3', '2', '3']
The reason the object you have is not iterable is because it is not a string. It is a single number, i.e an integer.
If you on the other hand, had a string, say
babe = '122132323'
b = [n for n in babe]
print b
It will print
['1', '2', '2', '1', '3', '2', '3', '2', '3']
To iterate on an integer value, you need n for n in range (babe). That tells Python to use the numbers from zero to babe-1 as loop counter values. Assuming you want to have an actual number, of course...
What values of n are you looking for?
1, 2, 2, 1, 3, 2, 3, 2, 3
or
1, 2, 3, 4, ..., 122132323?
For the first you need
[n for n in '122132323']
and for the second you need
n for n in range(babe)]
(or just list(range(babe)).
Related
I am trying t convert a number as follows:
input -> 123456
output -> ['1','2','3','4','5','6']
The following loop does work:
number = 123456
defg = []
abc = str(number)
for i in range(len(abc)):
defg.append(abc[i])
However, when i try this in the form of a one line for loop, the output is ['None','None','None','None']
My one line loop is as follows:
number = 123456
defg = []
abc = str(number)
defg= [[].append(abc[i]) for i in range(len(abc))]
Any idea what I am doing wrong?
The answers above are concise, but I personally prefer vanilla list comprehension over map, as powerful as it is. I add this answer simply for the sake of adding diversity to the mix, showing that the same can be achieved without using map.
str_list = [abc[i] for i in range(len(abc))]
We can strive for a more Pythonic solution by avoiding direct indexing and using a simpler loop.
better_str_list = [char for char in abc]
This list comprehension is basically just a translation of the for loop you already have.
Try this:
x = 527876324
print(list(str(x))
Output
['5', '2', '7', '8', '7', '6', '3', '2', '4']
here the solution
list(map(lambda x: str(x), str(number)))
Out[13]: ['1', '2', '3', '4', '5', '6']
or you can do this
list(map(str, str(number)))
Out[13]: ['1', '2', '3', '4', '5', '6']
or this
list(str(number))
['1', '2', '3', '4', '5', '6']
duplicate you can see more here
Splitting integer in Python?
Solution
As your expection the result is
number = 123456
defg = []
abc = str(number)
[defg.append(abc[i]) for i in range(len(abc))]
print(defg)
When you run the loop the values are append to defg but it return none. you assign the None value to defg so it will show the None output
Recomanded way
You can use list metnod to convert the number to list
number = 865393410
result = list(str(number))
print(result)
If you want int in list try this
number = 865393410
result = []
for i in list(str(number)):
result.append(int(i))
print(result)
With single line loop
number = 865393410
result = []
[result.append(int(i)) for i in list(str(number))]
print(result)
The last one is recommended for you
I'm having some trouble converting type 'str' to numbers. I use a separate text-file containing the following numbers 1, 2, 3, 4, 5, 6 and then I import these numbers into python and save them as a list. However, by doing this, I get a list of strings as follows: ['1', '2', '3', '4', '5', '6']. I want to convert this list of strings so the list represents numbers, i.e. the output should be [1, 2, 3, 4, 5, 6].
My code is:
def imported_numbers(filename):
with open(filename, 'r') as f:
contents = f.read().splitlines()
print(contents)
imported_numbers('sample.txt')
Is there a specific command to do this?
IMO it's more pythonic to say
str_list = ['1', '2', '3']
new_list = [int(n) for n in str_list]
If you're not sure all of the strings will be valid numbers, you need to add appropriate error handling.
You can use map:
l = ['1', '2', '3', '4', '5', '6']
new_l = list(map(int, l)) # or just map(int, l) in Python 2
will return
[1, 2, 3, 4, 5, 6]
This can throw an error if there are strings that cannot be converted to numbers though:
l = ['1', '2', '3', '4', '5', 'lkj']
list(map(int, l))
ValueError: invalid literal for int() with base 10: 'lkj'
So make sure your input is valid and/or wrap it into a try/except.
All,
I've recently picked up Python and currently in the process of dealing with lists. I'm using a test file containing several lines of characters indented by a tab and then passing this into my python program.
The aim of my python script is to insert each line into a list using the length as the index which means that the list would be automatically sorted. I am considering the most basic case and am not concerned about any complex cases.
My python code below;
newList = []
for line in sys.stdin:
data = line.strip().split('\t')
size = len(data)
newList.insert(size, data)
for i in range(len(newList)):
print ( newList[i])
My 'test' file below;
2 2 2 2
1
3 2
2 3 3 3 3
3 3 3
My expectation of the output of the python script is to print the contents of the list in the following order sorted by length;
['1']
['3', '2']
['3', '3', '3']
['2', '2', '2', '2']
['2', '3', '3', '3', '3']
However, when I pass in my test file to my python script, I get the following;
cat test | ./listSort.py
['2', '2', '2', '2']
['1']
['3', '2']
['3', '3', '3']
['2', '3', '3', '3', '3']
The first line of the output ['2', '2', '2', '2'] is incorrect. I'm trying to figure out why it isn't being printed at the 4th line (because of length 4 which would mean that it would have been inserted into the 4th index of the list). Could someone please provide some insight into why this is? My understanding is that I am inserting each 'data' into the list using 'size' as the index which means when I print out the contents of the list, they would be printed in sorted order.
Thanks in advance!
Inserting into lists work quite differently than what you think:
>>> newList = []
>>> newList.insert(4, 4)
>>> newList
[4]
>>> newList.insert(1, 1)
>>> newList
[4, 1]
>>> newList.insert(2, 2)
>>> newList
[4, 1, 2]
>>> newList.insert(5, 5)
>>> newList
[4, 1, 2, 5]
>>> newList.insert(3, 3)
>>> newList
[4, 1, 2, 3, 5]
>>> newList.insert(0, 0)
>>> newList
[0, 4, 1, 2, 3, 5]
Hopefully you can see two things from this example:
The list indices are 0-based. That is to say, the first entry has index 0, the second has index 1, etc.
list.insert(idx, val) inserts things into the position which currently has index idx, and bumps everything after that down a position. If idx is larger than the current length of the list, the new item is silently added in the last position.
There are several ways to implement the functionality you want:
If you can predict the number of lines, you can allocate the list beforehand, and simply assign to the elements of the list instead of inserting:
newList = [None] * 5
for line in sys.stdin:
data = line.strip().split('\t')
size = len(data)
newList[size - 1] = data
for i in range(len(newList)):
print ( newList[i])
If you can predict a reasonable upper bound of the number of lines, you can also do this, but you need to have some way to remove the None entries afterwards.
Use a dictionary:
newList = {}
for line in sys.stdin:
data = line.strip().split('\t')
size = len(data)
newList[size - 1] = data
for i in range(len(newList)):
print ( newList[i])
Add elements to the list as necessary, which is probably a little bit more involved:
newList = []
for line in sys.stdin:
data = line.strip().split('\t')
size = len(data)
if len(newList) < size: newList.extend([None] * (size - len(newList)))
newList[size - 1] = data
for i in range(len(newList)):
print ( newList[i])
I believe I've figured out the answer to my question, thanks to mkrieger1. I append to the list and then sort it using the length as the key;
newList = []
for line in sys.stdin:
data = line.strip().split('\t')
newList.append(data)
newList.sort(key=len)
for i in range(len(newList)):
print (newList[i])
I got the output I wanted;
/listSort.py < test
['1']
['3', '2']
['3', '3', '3']
['2', '2', '2', '2']
['2', '3', '3', '3', '3']
I am having a list which contains some elements with repetition and from this list I want to generate a list which has no repeated elements in it AND also maintains theie Order in the List.
I tried set(['1','1','2','3','4','4','5','2','2','3','3','6']) and got the output as set(['1', '3', '2', '5', '4', '6'])
But I want the output as set(['1', '2', '3', '4', '5', '6']) i.e. maintain the relative order of the elements already present.
How to do this??? Thanks in advance...
One way to do this:
In [9]: x = ['1','1','2','3','4','4','5','2','2','3','3','6']
In [10]: s = set()
In [11]: y = []
In [12]: for i in x:
...: if i not in s:
...: y.append(i)
...: s.add(i)
...:
In [13]: y
Out[13]: ['1', '2', '3', '4', '5', '6']
As noted by Martijn, a set is unordered by definition, so you need a list to store the result. See also this old question.
Starting with two lists such as:
lstOne = [ '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
lstTwo = [ '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
I want to have the user input how many items they want to extract, as a percentage of the overall list length, and the same indices from each list to be randomly extracted. For example say I wanted 50% the output would be
newLstOne = ['8', '1', '3', '7', '5']
newLstTwo = ['8', '1', '3', '7', '5']
I have achieved this using the following code:
from random import randrange
lstOne = [ '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
lstTwo = [ '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
LengthOfList = len(lstOne)
print LengthOfList
PercentageToUse = input("What Percentage Of Reads Do you want to extract? ")
RangeOfListIndices = []
HowManyIndicesToMake = (float(PercentageToUse)/100)*float(LengthOfList)
print HowManyIndicesToMake
for x in lstOne:
if len(RangeOfListIndices)==int(HowManyIndicesToMake):
break
else:
random_index = randrange(0,LengthOfList)
RangeOfListIndices.append(random_index)
print RangeOfListIndices
newlstOne = []
newlstTwo = []
for x in RangeOfListIndices:
newlstOne.append(lstOne[int(x)])
for x in RangeOfListIndices:
newlstTwo.append(lstTwo[int(x)])
print newlstOne
print newlstTwo
But I was wondering if there was a more efficient way of doing this, in my actual use case this is subsampling from 145,000 items. Furthermore, is randrange sufficiently free of bias at this scale?
Thank you
Q. I want to have the user input how many items they want to extract, as a percentage of the overall list length, and the same indices from each list to be randomly extracted.
A. The most straight-forward approach directly matches your specification:
percentage = float(raw_input('What percentage? '))
k = len(data) * percentage // 100
indicies = random.sample(xrange(len(data)), k)
new_list1 = [list1[i] for i in indicies]
new_list2 = [list2[i] for i in indicies]
Q. in my actual use case this is subsampling from 145,000 items. Furthermore, is randrange sufficiently free of bias at this scale?
A. In Python 2 and Python 3, the random.randrange() function completely eliminates bias (it uses the internal _randbelow() method that makes multiple random choices until a bias-free result is found).
In Python 2, the random.sample() function is slightly biased but only in the round-off in the last of 53 bits. In Python 3, the random.sample() function uses the internal _randbelow() method and is bias-free.
Just zip your two lists together, use random.sample to do your sampling, then zip again to transpose back into two lists.
import random
_zips = random.sample(zip(lstOne,lstTwo), 5)
new_list_1, new_list_2 = zip(*_zips)
demo:
list_1 = range(1,11)
list_2 = list('abcdefghij')
_zips = random.sample(zip(list_1, list_2), 5)
new_list_1, new_list_2 = zip(*_zips)
new_list_1
Out[33]: (3, 1, 9, 8, 10)
new_list_2
Out[34]: ('c', 'a', 'i', 'h', 'j')
The way you are doing it looks mostly okay to me.
If you want to avoid sampling the same object several times, you could proceed as follows:
a = len(lstOne)
choose_from = range(a) #<--- creates a list of ints of size len(lstOne)
random.shuffle(choose_from)
for i in choose_from[:a]: # selects the desired number of items from both original list
newlstOne.append(lstOne[i]) # at the same random locations & appends to two newlists in
newlstTwo.append(lstTwo[i]) # sequence