Search code examples
pythonpython-3.xmapreduce

Use sys.stdin to compare 2 lins in python?

I am using python to do my MapReduce homework which will use sys.stdin as a reader of the input file. for example :

for line in sys.stdin:
     # compare 1st line with the 2ed line.

I can load all the file content into memory and use the index to implement a 2 lines comparasion for exmample:

lines= open("guru99.txt","r")
for i in range(len(lines)):
    if lines[i] != lines[i-1]:
       ...

My question is How to do these 2 lines comparison using sys.stdin way? As the homework file "guru99.txt" is huge and I can't load it into memory but only the sys.stdin way will work.

Solution

  • You can get the first line using next and then iterate the remaining input.

    import sys

try:
    prev = next(sys.stdin)
except StopIteration:
    # no input
    exit()

for line in sys.stdin:
    if line == prev:
        do the things
    prev = line