After I read from file:
with open(fileName) as f:
for line in f:
print(line.split(",")) #split the file into multiple lists
How do I get some specific element(s) from those lists?
For example, only elements with index[0 to 3], but discard/ignore any elements after that.
If you want to save the first three items in each line, you could use a list comprehension
with open(fileName) as f:
firstitems = [line.rstrip().split(",")[0:3] for line in f]
Note that the rstrip() is needed to remove the final newline character, if there are fewer than four items in a line. Note that the "items" are all strings, even if they look like other types. If you want integers, for example, you will need to convert them to integers.
Then you can print them:
for line in firstitems:
print(line)
Try the below code:
with open('f.txt') as f:
print('\n'.join([i for i in f.read().split(',')[0:3]]))
Related
I have a function gen_rand_index that generates a random group of numbers in list format, such as [3,1] or [3,2,1]
I also have a textfile that that reads something like this:
red $1
green $5
blue $6
How do I write a function so that once python generates this list of numbers, it automatically reads that # line in the text file? So if it generated [2,1], instead of printing [2,1] I would get "green $5, red $1" aka the second line in the text file and the first line in the text file?
I know that you can do print(line[2]) and commands like that, but this won't work in my case because each time I am getting a different random number of a line that I want to read, it is not a set line I want to read each time.
row = str(result[gen_rand_index]) #result[gen_rand_index] gives me the random list of numbers
file = open("Foodinventory.txt", 'r')
for line in file:
print(line[row])
file.close()
I have this so far, but I am getting this
error: invalid literal for int() with base 10: '[4, 1]'
I also have gotten
TypeError: string indices must be integers
butI have tried replacing str with int and many things like that but I'm thinking the way I'm just approaching this is wrong. Can anyone help me? (I have only been coding for a couple days now so I apologize in advance if this question is really basic)
Okay, let us first get some stuff out of the way
Whenever you access something from a list the thing you put inside the box brackets [] should be an integer, eg: [5]. This tells Python that you want the 5th element. It cannot ["5"] because 5 in this case would be treated as a string
Therefore the line row = str(result[gen_rand_index]) should actually just be row = ... without the call to str. This is why you got the TypeError about list indices
Secondly, as per your description gen_rand_index would return a list of numbers.
So going by that, why don;t you try this
indices_to_pull = gen_rand_index()
file_handle = open("Foodinventory.txt", 'r')
file_contents = file_handle.readlines() # If the file is small and simle this would work fine
answer = []
for index in indices_to_pull:
answer.append(file_contents[index-1])
Explanation
We get the indices of the file lines from gen_rand_index
we read the entire file into memory using readlines()
Then we get the lines we want, Rememebr to subtract 1 as the list is indexed from 0
The error you are getting is because you're trying to index a string variable (line) with a string index (row). Presumably row will contain something like '[2,3,1]'.
However, even if row was a numerical index, you're not indexing what you think you're indexing. The variable line is a string, and it contains (on any given iteration) one line of the file. Indexing this variable will give you a single character. For example, if line contains green $5, then line[2] will yield 'e'.
It looks like your intent is to index into a list of strings, which represent all the lines of the file.
If your file is not overly large, you can read the entire file into a list of lines, and then just index that array:
with open('file.txt') as fp:
lines = fp.readlines()
print(lines[2]).
In this case, lines[2] will yield the string 'blue $6\n'.
To discard the trailing newline, use lines[2].strip() instead.
I'll go line by line and raise some issues.
row = str(result[gen_rand_index]) #result[gen_rand_index] gives me the random list of numbers
Are you sure it is gen_rand_index and not gen_rand_index()? If gen_rand_index is a function, you should call the function. In the code you have, you are not calling the function, instead you are using the function directly as an index.
file = open("Foodinventory.txt", 'r')
for line in file:
print(line[row])
file.close()
The correct python idiom for opening a file and reading line by line is
with open("Foodinventory.txt.", "r") as f:
for line in f:
...
This way you do not have to close the file; the with clause does this for you automatically.
Now, what you want to do is to print the lines of the file that correspond to the elements in your variable row. So what you need is an if statement that checks if the line number you just read from the file corresponds to the line number in your array row.
with open("Foodinventory.txt", "r") as f:
for i, line in enumerate(f):
if i == row[i]:
print(line)
But this is wrong: it would work only if your list's elements are ordered. That is not the case in your question. So let's think a little bit. You could iterate over your file multiple times, and each time you iterate over it, print out one line. But this will be inefficient: it will take time O(nm) where n==len(row) and m == number of lines in your file.
A better solution is to read all the lines of the file and save them to an array, then print the corresponding indices from this array:
arr = []
with open("Foodinventory.txt", "r") as f:
arr = list(f)
for i in row:
print(arr[i - 1]) # arrays are zero-indiced
i want to generate a list of server addresses and credentials reading from a file, as a single list splitting from newline in file.
file is in this format
login:username
pass:password
destPath:/directory/subdir/
ip:10.95.64.211
ip:10.95.64.215
ip:10.95.64.212
ip:10.95.64.219
ip:10.95.64.213
output i want is in this manner
[['login:username', 'pass:password', 'destPath:/directory/subdirectory', 'ip:10.95.64.211;ip:10.95.64.215;ip:10.95.64.212;ip:10.95.64.219;ip:10.95.64.213']]
i tried this
with open('file') as f:
credentials = [x.strip().split('\n') for x in f.readlines()]
and this returns lists within list
[['login:username'], ['pass:password'], ['destPath:/directory/subdir/'], ['ip:10.95.64.211'], ['ip:10.95.64.215'], ['ip:10.95.64.212'], ['ip:10.95.64.219'], ['ip:10.95.64.213']]
am new to python, how can i split by newline character and create single list. thank you in advance
You could do it like this
with open('servers.dat') as f:
L = [[line.strip() for line in f]]
print(L)
Output
[['login:username', 'pass:password', 'destPath:/directory/subdir/', 'ip:10.95.64.211', 'ip:10.95.64.215', 'ip:10.95.64.212', 'ip:10.95.64.219', 'ip:10.95.64.213']]
Just use a list comprehension to read the lines. You don't need to split on \n as the regular file iterator reads line by line. The double list is a bit unconventional, just remove the outer [] if you decide you don't want it.
I just noticed you wanted the list of ip addresses joined in one string. It's not clear as its off the screen in the question and you make no attempt to do it in your own code.
To do that read the first three lines individually using next then just join up the remaining lines using ; as your delimiter.
def reader(f):
yield next(f)
yield next(f)
yield next(f)
yield ';'.join(ip.strip() for ip in f)
with open('servers.dat') as f:
L2 = [[line.strip() for line in reader(f)]]
For which the output is
[['login:username', 'pass:password', 'destPath:/directory/subdir/', 'ip:10.95.64.211;ip:10.95.64.215;ip:10.95.64.212;ip:10.95.64.219;ip:10.95.64.213']]
It does not match your expected output exactly as there is a typo 'destPath:/directory/subdirectory' instead of 'destPath:/directory/subdir' from the data.
This should work
arr = []
with open('file') as f:
for line in f:
arr.append(line)
return [arr]
You could just treat the file as a list and iterate through it with a for loop:
arr = []
with open('file', 'r') as f:
for line in f:
arr.append(line.strip('\n'))
I've already tried:
with open('names.txt', 'r') as f:
myNames = f.readlines()
And multiple other ways that I have found on stack overflow but they are not doing exactly what I need.
I have a text file that has one line with multiple words ex:
FLY JUMP RUN
I need these in a list but for them to be separate elements in the list like:
['FLY', 'JUMP', 'RUN']
Except when using the the methods I find on stack overflow, I get:
['FLY JUMP RUN']
But I need them to be separate because I am using the random.choice method on the list.
As was mentioned in the comments, you should try
myNames = None
with open('names.txt', 'r') as f:
myNames = f.read().split()
Assuming the file is written the way you say. Of course it won't matter as the default behaviour of split() is to split the string, using whitespace characters like spaces, and newline characters, so if your file consists of
One Two
Three
then
f.read().split()
will still return
["One", "Two", "Three"]
#Trey: To answer your comment.
No. readlines() will read all the contents of the file into a single list while read() simply reads it as a single strring.
Try this code:
with open('names.txt', 'r') as f:
myNames = f.read().split() #split by space
This will work as you expected for any type of data, as long as the words in a line is space separated.
I have a text file that looks like this:
(1064.2966,1898.787,1064.2986,1898.787,1064.2986,1898.785,1064.2966,1898.785)
(1061.0567,1920.3816,1065.1361,1920.2276,1065.5847,1915.9657,1065.4726,1915.2927,1061.0985,1914.3955,1058.1824,1913.9468,1055.6028,1913.9468,1051.0044,1916.19,1051.5651,1918.8817,1056.0514,1918.9939,1058.9675,1919.6668,1060.8741,1920.4519)
etc (all rows have different lengths)
when I use
np.loadtxt(filename,dtype=float,delimiter=',')
I get
ValueError: could not convert string to float: (1031.4647
I think np.loadtxt expects numbers so it does not know how to convert a value which starts with a '(', I think you have two choices here:
lines = []
with open('datafile') as infile:
for line in infile:
line = line.rstrip('\n')[1:-1] # this removes first and last parentheses from the line
lines.append([float(v) for v in line.split(',')])
in this way you end up with lines which is a list of lists of values (i.e. lines[0] is a list of the values on line 1).
The other way to go is modifying the data file to remove the parentheses, which you can do in many ways depending on the platform you are working on.
In most Linux systems for instance you can just do something along the lines of this answer
EDIT: as suggested by #AlexanderHuszagh in the comments section, different systems can have different ways of representing newlines, so a more robust solution would be:
lines = []
with open('datafile') as infile:
file_lines = infile.read().splitlines()
for line in file_lines:
lines.append([float(v) for v in line[1:-1].split(',')])
You got the error because of the parentheses, you can replace it this way:
s = open(filename).read().replace('(','').replace(')','')
This return a list of arrays:
arrays = [np.array(map(float, line.split(","))) for line in s.split("\n")]
This question already has answers here:
How to read a file line-by-line into a list?
(28 answers)
Why does this iterative list-growing code give IndexError: list assignment index out of range? How can I repeatedly add (append) elements to a list?
(9 answers)
Closed 7 months ago.
I'm trying to open a file and create a list with each line read from the file.
i=0
List=[""]
for Line in inFile:
List[i]=Line.split(",")
i+=1
print List
But this sample code gives me an error because of the i+=1 saying that index is out of range.
What's my problem here? How can I write the code in order to increment my list with every new Line in the InFile?
It's a lot easier than that:
List = open("filename.txt").readlines()
This returns a list of each line in the file.
I did it this way
lines_list = open('file.txt').read().splitlines()
Every line comes with its end of line characters (\n\r); this way the characters are removed.
my_list = [line.split(',') for line in open("filename.txt")]
Please read PEP8. You're swaying pretty far from python conventions.
If you want a list of lists of each line split by comma, I'd do this:
l = []
for line in in_file:
l.append(line.split(','))
You'll get a newline on each record. If you don't want that:
l = []
for line in in_file:
l.append(line.rstrip().split(','))
A file is almost a list of lines. You can trivially use it in a for loop.
myFile= open( "SomeFile.txt", "r" )
for x in myFile:
print x
myFile.close()
Or, if you want an actual list of lines, simply create a list from the file.
myFile= open( "SomeFile.txt", "r" )
myLines = list( myFile )
myFile.close()
print len(myLines), myLines
You can't do someList[i] to put a new item at the end of a list. You must do someList.append(i).
Also, never start a simple variable name with an uppercase letter. List confuses folks who know Python.
Also, never use a built-in name as a variable. list is an existing data type, and using it as a variable confuses folks who know Python.
f.readlines() returns a list that contains each line as an item in the list
if you want eachline to be split(",") you can use list comprehensions
[ list.split(",") for line in file ]
Assuming you also want to strip whitespace at beginning and end of each line, you can map the string strip function to the list returned by readlines:
map(str.strip, open('filename').readlines())
... Also If you want to get rid of \n
In case the items on your list are with \n and you want to get rid of them:
with open('your_file.txt') as f:
list= f.read().splitlines()
I am not sure about Python but most languages have push/append function for arrays.