仅保留一个文本文件中的特定字符并将它们写入新的文本文件

Question

我想选择特定的字符。说文件old.txt包含xxXXyyaasdyyYY。从该文件中只应保留X和Y并写入new.txt。 下面的代码有什么错误？

in_file = open("old.txt", "r") 
out_file = open("new.txt","w") 
for line in in_file: 
    out_file.write(line.upper()) 
in_file.close() 
out_file.close() 

Answer 1

既然你要选择的字符，你可以一次读取一个字符。

from collections import defaultdict 

specific_characters = ['X', 'Y'] 
counter_dict = defaultdict(lambda: 0) 

with open("old.txt", "r") as in_file, open("new.txt","a") as out_file: 
    while True: 
    c = in_file.read(1) 
    if not c: 
     break 
    if c in specific_characters: 
     out_file.write(c) 
     counter_dict[c] += 1 

# printing just X and Y for your specific case. 
# the counter will have count of any characters from the specific_characters list. 

print "Count of X: ", counter_dict['X'] 
print "Count of Y: ", counter_dict['Y'] 

Answer 2

你可以使用白名单set和上下文管理器（使用with关键字），使这个更加地道。

whitelist = {"X", "Y"} 

with open('old.txt') as in_file, 
     open('new.txt', 'w') as out_file: 
    for line in in_file: 
     for letter in line: 
      if letter in whitelist: 
       out_file.write(letter) # no need to uppercase here 
# no need to close either, since we're using the with statement 

Answer 3

in_file = open("old.txt", "r") 
out_file = open("new.txt","w") 
for line in in_file: 
    for letter in line: 
    if (letter == 'X') | (letter == 'Y'): 
     out_file.write(letter.upper()) 
in_file.close() 
out_file.close()