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Calculating with data from a txt file in python

Detailed:
I have a set of 200 or so values in a txt file and I want to select the first value b[0] and then go through the list from [1] to [199] and add them together.
So, [0]+[1]
if that's not equal to a certain number, then it would go to the next term i.e. [0]+[2] etc etc until it's gone through every term. Once it's done that it will increase b[0] to b[1] and then goes through all the values again
Step by step:
Select first number in list.
Add that number to the next number
Check if that equals a number
If it doesn't, go to next term and add to first term
Iterate through these until you've gone through all terms/ found
a value which adds to target value
If gone through all values, then go to the next term for the
starting add value and continue
I couldn't get it to work, if anyone can maybe provide a solution or give some advice? Much appreciated. I've tried looking at videos and other stack overflow problems but I still didn't get anywhere. Maybe I missed something, let me know! Thank you! :)
I've attempted it but gotten stuck. This is my code so far:
b = open("data.txt", "r")
data_file = open("data.txt", "r")
for i, line in enumerate(data_file):
if (i+b)>2020 or (i+b)<2020:
b=b+1
else:
print(i+b)
print(i*b)
Error:
Traceback (most recent call last):
File "c:\Users\███\Desktop\ch1.py", line 11, in <module>
if (i+b)>2020 or (i+b)<2020:
TypeError: unsupported operand type(s) for +: 'int' and '_io.TextIOWrapper'
PS C:\Users\███\Desktop>

I would read the file into an array and then convert it into ints before
actually dealing with the problem. files are messy and the less we have to deal with them the better
with open("data.txt", "r") as data_file:
lines = data_file.readlines() # reads the file into an array
data_file.close
j = 0 # you could use a better much more terse solution but this is easy to understand
for i in lines:
lines[j] = int(i.strip().replace("\n", ""))
j += 1
i, j = 0
for i in lines: # for every value of i we go through every value of j
# so it would do x = [0] + [0] , [0] + [1] ... [1] + [0] .....
for j in lines:
x = j + i
if x == 2020:
print(i * j)

Here are some things that you can fix.
You can't add the file object b to the integer i. You have to convert the lines to int by using something like:
integer_in_line = int(line.strip())
Also you have opened the same file twice in read mode with:
b = open("data.txt", "r")
data_file = open("data.txt", "r")
Opening it once is enough.
Make sure that you close the file after you used it:
data_file.close()
To compare each number in the list with each other number in the list you'll need to use a double for loop. Maybe this works for you:
certain_number = 2020
data_file = open("data.txt", "r")
ints = [int(line.strip()) for line in data_file] # make a list of all integers in the file
for i, number_at_i in enumerate(ints): # loop over every integer in the list
for j, number_at_j in enumerate(ints): # loop over every integer in the list
if number_at_i + number_at_j == certain_number: # compare the integers to your certain number
print(f"{number_at_i} + {number_at_j} = {certain_number}")
data_file.close()

Your problem is the following: The variables b and data_file are not actually the text that you are hoping they are. You should read something about reading text files in python, there are many tutorials on that.
When you call open("path.txt", "r"), the open function returns a file object, not your text. If you want the text from the file, you should either call read or readlines. Also it is important to close your file after reading the content.
data_file = open("data.txt", "r") # b is a file object
text = data_file.read() # text is the actual text in the file in a single string
data_file.close()
Alternatively, you could also read the text into a list of strings, where each string represents one line in the file: lines = data_file.readlines().
I assume that your "data.txt" file contains one number per line, is that correct? In that case, your lines variable will be a list of the numbers, but they will be strings, not integers or floats. Therefore, you can't simply use them to perform calculation. You would need to call int() on them.
Here is an example how to do it. I assumed that your textfile looks like this (with arbitary numbers):
1
2
3
4
...
file = open("data.txt", "r")
lines = file.readlines()
file.close()
# This creates a new list where the numbers are actual numbers and not strings
numbers = []
for line in lines:
numbers.append(int(line))
target_number = 2020
starting_index = 0
found = False
for i in range(starting_index, len(numbers)):
temp = numbers[i]
for j in range(i + 1, len(numbers)):
temp += numbers[j]
if temp == target_number:
print(f'Target number reached by adding nubmers from {i} to {j}')
found = True
break #This stops the inner loop.
if found:
break #This stops the outer loop

Error with .readlines()[n]

I'm a beginner with Python.
I tried to solve the problem: "If we have a file containing <1000 lines, how to print only the odd-numbered lines? ". That's my code:
with open(r'C:\Users\Savina\Desktop\rosalind_ini5.txt')as f:
n=1
num_lines=sum(1 for line in f)
while n<num_lines:
if n/2!=0:
a=f.readlines()[n]
print(a)
break
n=n+2
where n is a counter and num_lines calculates how many lines the file contains.
But when I try to execute the code, it says:
"a=f.readlines()[n]
IndexError: list index out of range"
Why it doesn't recognize n as a counter?

You have the call to readlines into a loop, but this is not its intended use,
because readlines ingests the whole of the file at once, returning you a LIST
of newline terminated strings.
You may want to save such a list and operate on it
list_of_lines = open(filename).readlines() # no need for closing, python will do it for you
odd = 1
for line in list_of_lines:
if odd : print(line, end='')
odd = 1-odd
Two remarks:
odd is alternating between 1 (hence true when argument of an if) or 0 (hence false when argument of an if),
the optional argument end='' to the print function is required because each line in list_of_lines is terminated by a new line character, if you omit the optional argument the print function will output a SECOND new line character at the end of each line.
Coming back to your code, you can fix its behavior using a
f.seek(0)
before the loop to rewind the file to its beginning position and using the
f.readline() (look, it's NOT readline**S**) method inside the loop,
but rest assured that proceding like this is. let's say, a bit unconventional...
Eventually, it is possible to do everything you want with a one-liner
print(''.join(open(filename).readlines()[::2]))
that uses the slice notation for lists and the string method .join()

Well, I'd personally do it like this:
def print_odd_lines(some_file):
with open(some_file) as my_file:
for index, each_line in enumerate(my_file): # keep track of the index of each line
if index % 2 == 1: # check if index is odd
print(each_line) # if it does, print it
if __name__ == '__main__':
print_odd_lines('C:\Users\Savina\Desktop\rosalind_ini5.txt')
Be aware that this will leave a blank line instead of the even number. I'm sure you figure how to get rid of it.

This code will do exactly as you asked:
with open(r'C:\Users\Savina\Desktop\rosalind_ini5.txt')as f:
for i, line in enumerate(f.readlines()): # Iterate over each line and add an index (i) to it.
if i % 2 == 0: # i starts at 0 in python, so if i is even, the line is odd
print(line)
To explain what happens in your code:
A file can only be read through once. After that is has to be closed and reopened again.
You first iterate over the entire file in num_lines=sum(1 for line in f). Now the object f is empty.
If n is odd however, you call f.readlines(). This will go through all the lines again, but none are left in f. So every time n is odd, you go through the entire file. It is faster to go through it once (as in the solutions offered to your question).

As a fix, you need to type
f.close()
f = open(r'C:\Users\Savina\Desktop\rosalind_ini5.txt')
everytime after you read through the file, in order to get back to the start.
As a side note, you should look up modolus % for finding odd numbers.

Python reading file and analysing lines with substring

In Python, I'm reading a large file with many many lines. Each line contains a number and then a string such as:
[37273738] Hello world!
[83847273747] Hey my name is James!
And so on...
After I read the txt file and put it into a list, I was wondering how I would be able to extract the number and then sort that whole line of code based on the number?
file = open("info.txt","r")
myList = []
for line in file:
line = line.split()
myList.append(line)
What I would like to do:
since the number in message one falls between 37273700 and 38000000, I'll sort that (along with all other lines that follow that rule) into a separate list

This does exactly what you need (for the sorting part)
my_sorted_list = sorted(my_list, key=lambda line: int(line[0][1:-2]))

Use tuple as key value:
for line in file:
line = line.split()
keyval = (line[0].replace('[','').replace(']',''),line[1:])
print(keyval)
myList.append(keyval)
Sort
my_sorted_list = sorted(myList, key=lambda line: line[0])

How about:
# ---
# Function which gets a number from a line like so:
# - searches for the pattern: start_of_line, [, sequence of digits
# - if that's not found (e.g. empty line) return 0
# - if it is found, try to convert it to a number type
# - return the number, or 0 if that conversion fails
def extract_number(line):
import re
search_result = re.findall('^\[(\d+)\]', line)
if not search_result:
num = 0
else:
try:
num = int(search_result[0])
except ValueError:
num = 0
return num
# ---
# Read all the lines into a list
with open("info.txt") as f:
lines = f.readlines()
# Sort them using the number function above, and print them
lines = sorted(lines, key=extract_number)
print ''.join(lines)
It's more resilient in the case of lines without numbers, it's more adjustable if the numbers might appear in different places (e.g. spaces at the start of the line).
(Obligatory suggestion not to use file as a variable name because it's a builtin function name already, and that's confusing).
Now there's an extract_number() function, it's easier to filter:
lines2 = [L for L in lines if 37273700 < extract_number(L) < 38000000]
print ''.join(lines2)

How to make lists of integers from a portion of a file with Python?

I have a file which looks like the following:
# junk
...
# junk
1.0 -100.102487081243
1.1 -100.102497023421
... ...
3.0 -100.102473082342
&
# junk
...
I am interested only in the two columns of numbers given between the # and & characters. These characters may appear anywhere else in the file but never inside the number block.
I want to create two lists, one with the first column and one with the second column.
List1 = [1.0, 1.1,..., 3.0]
List2 = [-100.102487081243, -100.102497023421,..., -100.102473082342]
I've been using shell scripting to prep these files for a simpler Python script which makes lists, however, I'm trying to migrate these processes over to Python for a more consistent application. Any ideas? I have limited experience with Python and file handling.
Edit: I should mention, this number block appears in two places in the file. Both number blocks are identical.
Edit2: A general function would be most satisfactory for this as I will put it into a custom library.
Current Efforts
I currently use a shell script to trim out everything but the number block into two separate columns. From there it is trivial for me to use the following function
def ReadLL(infile):
List = open(infile).read().splitlines()
intL = [int(i) for i in List]
return intL
by calling it from my main
import sys
import eLIBc
infile = sys.argv[1]
sList = eLIBc.ReadLL(infile)
The problem is knowing how to extract the number block from the original file with Python rather than using shell scripting.

You want to loop over the file itself, and set a flag for when you find the first line without a # character, after which you can start collecting numbers. Break off reading when you find the & character on a line.
def readll(infile):
with open(infile) as data:
floatlist1, floatlist2 = [], []
reading = False
for line in data:
if not reading:
if '#' not in line:
reading = True
else:
continue
if '&' in line:
return floatlist1, floatlist2
numbers = map(float, line.split())
floatlist1.append(numbers[0])
floatlist2.append(numbers[1])
So the above:
sets 'reading' to False, and only when a line without '#' is found, is that set to True.
when 'reading' is True:
returns the data read if the line contains &
otherwise it's assumed the line contains two float values separated by whitespace, which are added to their respective lists
By returning, the function ends, with the file closed automatically. Only the first block is read, the rest of the file is simply ignored.

Try this out:
with open("i.txt") as fp:
lines = fp.readlines()
data = False
List1 = []
List2 = []
for line in lines:
if line[0] not in ['&', '#']:
print line
line = line.split()
List1.append(line[0])
List2.append(line[1])
data = True
elif data == True:
break
print List1
print List2
This should give you the first block of numbers.
Input:
# junk
# junk
1.0 -100.102487081243
1.1 -100.102497023421
3.0 -100.102473082342
&
# junk
1.0 -100.102487081243
1.1 -100.102497023421
Output:
['1.0', '1.1', '3.0']
['-100.102487081243', '-100.102497023421', '-100.102473082342']
Update
If you need both blocks, then use this:
with open("i.txt") as fp:
lines = fp.readlines()
List1 = []
List2 = []
for line in lines:
if line[0] not in ['&', '#']:
print line
line = line.split()
List1.append(line[0])
List2.append(line[1])
print List1
print List2

Python- how to use while loop to return longest line of code

I just started learning python 3 weeks ago, I apologize if this is really basic. I needed to open a .txt file and print the length of the longest line of code in the file. I just made a random file named it myfile and saved it to my desktop.
myfile= open('myfile', 'r')
line= myfile.readlines()
len(max(line))-1
#the (the "-1" is to remove the /n)
Is this code correct? I put it in interpreter and it seemed to work OK.
But I got it wrong because apparently I was supposed to use a while loop. Now I am trying to figure out how to put it in a while loop. I've read what it says on python.org, watched videos on youtube and looked through this site. I just am not getting it. The example to follow that was given is this:
import os
du=os.popen('du/urs/local')
while 1:
line= du.readline()
if not line:
break
if list(line).count('/')==3:
print line,

print max([len(line) for line in file(filename).readlines()])

Taking what you have and stripping out the parts you don't need
myfile = open('myfile', 'r')
max_len = 0
while 1:
line = myfile.readline()
if not line:
break
if len(line) # ... somethin
# something
Note that this is a crappy way to loop over a file. It relys on the file having an empty line at the end. But homework is homework...

max(['b','aaa']) is 'b'
This lexicographic order isn't what you want to maximise, you can use the key flag to choose a different function to maximise, like len.
max(['b','aaa'], key=len) is 'aaa'
So the solution could be: len ( max(['b','aaa'], key=len) is 'aaa' ).
A more elegant solution would be to use list comprehension:
max ( len(line)-1 for line in myfile.readlines() )
.
As an aside you should enclose opening a file using a with statement, this will worry about closing the file after the indentation block:
with open('myfile', 'r') as mf:
print max ( len(line)-1 for line in mf.readlines() )

As other's have mentioned, you need to find the line with the maximum length, which mean giving the max() function a key= argument to extract that from each of lines in the list you pass it.
Likewise, in a while loop you'd need to read each line and see if its length was greater that the longest one you had seen so far, which you could store in a separate variable and initialize to 0 before the loop.
BTW, you would not want to open the file with os.popen() as shown in your second example.

I think it will be easier to understand if we keep it simple:
max_len = -1 # Nothing was read so far
with open("filename.txt", "r") as f: # Opens the file and magically closes at the end
for line in f:
max_len = max(max_len, len(line))
print max_len
As this is homework... I would ask myself if I should count the line feed character or not. If you need to chop the last char, change len(line) by len(line[:-1]).
If you have to use while, try this:
max_len = -1 # Nothing was read
with open("t.txt", "r") as f: # Opens the file
while True:
line = f.readline()
if(len(line)==0):
break
max_len = max(max_len, len(line[:-1]))
print max_len

For those still in need. This is a little function which does what you need:
def get_longest_line(filename):
length_lines_list = []
open_file_name = open(filename, "r")
all_text = open_file_name.readlines()
for line in all_text:
length_lines_list.append(len(line))
max_length_line = max(length_lines_list)
for line in all_text:
if len(line) == max_length_line:
return line.strip()
open_file_name.close()