Python. How to dynamically create variables based on number of lines in a file?

Question

Is it possible to create variables based on the number of lines in a file?

For example, assuming the file will always have an even-number of lines. If the file has 4 lines I want to create 2 variables. var1 will contain the first 2 lines and var2 will contain the following 2 lines. If the file has 10 lines I want to create 5 variables. Again the first var will have the first 2 lines, and the next var will have the following 2 lines and so on...

It's certainly possible, but... why do you want to do this? How do you imagine you'll use these variables? — Nathan Vērzemnieks, Jan 30 '18 at 05:51
"How do I dynamically create variables" is a very common beginner question, but the sane answer is almost always "use a dict" or "use a list". Search for duplicates. — tripleee, Jan 30 '18 at 05:59
Possible duplicate of [generating variable names on fly in python](https://stackoverflow.com/questions/4010840/generating-variable-names-on-fly-in-python) — tripleee, Jan 30 '18 at 06:00

score 0 · Accepted Answer · edited Jan 30 '18 at 06:09

It is almost always a bad idea to create variable names based on some programmatic value. Instead use a native data structure. In this case it sounds like a list is what you need.

Here is a way to loop through a file and collect pairs of lines into a list of lists.

var = []
last_line = None
for line in open('data.txt', 'rU'):
    if last_line:
        var.append([last_line, line.strip()])
        last_line = None
    else:
        last_line = line.strip()
if last_line:
    var.append([last_line])
print(var)

Results:

[['line1', 'line2'], ['line3', 'line4'], ['line5', 'line6']]

score 0 · Answer 2 · answered Jan 30 '18 at 06:09

from itertools import islice
num_lines = sum(1 for line in open('lines.txt'))
with open("lines.txt", "r+") as f:
    len_of_lines = num_lines
    count_ = 0
    while count_ < len_of_lines:
        var = list(islice(f, 2))
        # something with var
        print(var)
        count_ += 2
   >>>['xascdascac\n', 'ascascanscnas\n']
      ['ascaslkckaslca\n', 'ascascacac\n']
      ['ascascaca\n', 'ascacascaca\n']
      ['ascascascac\n']

Python. How to dynamically create variables based on number of lines in a file?

2 Answers2

Results: