学习python艰难的方式练习20我不知道它如何增加行号1,2,3

Question

from sys import argv

script, input_file = argv

def print_all(f):
    print f.read()

def rewind(f):
    f.seek(0)

def print_a_line(line_count, f):
    print line_count, f.readline()

current_file = open(input_file)

print "First let's print the whole file:\n"

print_all(current_file)

print "Now let's rewind, kind of like a tape."

rewind(current_file)

print "Let's print three lines:"

current_line = 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

current_line = current_line + 1
print_a_line(current_line, current_file)

Answer 1

current_line的初始值为1。当您致电current_line = current_line + 1时，我们首先评估=右侧的内容。这是current_line + 1，它会2。现在2被分配到=左侧的变量，即current_line。所以现在current_line是2！ <{1}}（current_line）的旧值会被覆盖。