对不复杂的列表进行不必要的修改

Question

here is the code:

with open('units.txt', 'r') as f:
   print(f.readlines())
   e = [elt.split(" ")[0] for elt in f.readlines()]
   print(f.readlines())

and here is the result:

['INPUT 0 2 #ffffff # # #\n', 'OUTPUT 2 0 #ffffff # # #\n', 'NOT 1 1 #ff0000 # # #\n', 'AND 2 1 #8888ee # # #\n', 'NAND 2 1 #ff00ff INPUT_OUTPUT_AND_NOT_ #3,0,_#0,0,_0,1,_#2,0,_# 0_3_2_1_']       
[] 

what am i missing?

Answer 1

You've already called readlines() on an open file. You need to reset the file pointer using file.seek(0) before calling it again.

Answer 2

You can't keep calling readlines on the file, because the first consumes the entire file then the rest doesn't read anything. Store it to a variable:

with open('units.txt', 'r') as f:
   lines = f.readlines()
   print(lines)
   e = [elt.split(" ")[0] for elt in lines]
   print(lines)

Alternatively, call f.seek(0) between calls to reset the file pointer, but storing to a variable is far cleaner.