如何一次从Python文件中读取单个字符？

谁能告诉我该怎么做？

with open(filename) as f:
  while True:
    c = f.read(1)
    if not c:
      print "End of file"
      break
    print "Read a character:", c

首先打开一个文件：

with open("filename") as fileobj:
    for line in fileobj:  
       for ch in line: 
           print ch

我喜欢公认的答案：这很简单，可以完成工作。我还想提供一个替代实现：

def chunks(filename, buffer_size=4096):
    """Reads `filename` in chunks of `buffer_size` bytes and yields each chunk
    until no more characters can be read; the last chunk will most likely have
    less than `buffer_size` bytes.

    :param str filename: Path to the file
    :param int buffer_size: Buffer size, in bytes (default is 4096)
    :return: Yields chunks of `buffer_size` size until exhausting the file
    :rtype: str

    """
    with open(filename, "rb") as fp:
        chunk = fp.read(buffer_size)
        while chunk:
            yield chunk
            chunk = fp.read(buffer_size)

def chars(filename, buffersize=4096):
    """Yields the contents of file `filename` character-by-character. Warning:
    will only work for encodings where one character is encoded as one byte.

    :param str filename: Path to the file
    :param int buffer_size: Buffer size for the underlying chunks,
    in bytes (default is 4096)
    :return: Yields the contents of `filename` character-by-character.
    :rtype: char

    """
    for chunk in chunks(filename, buffersize):
        for char in chunk:
            yield char

def main(buffersize, filenames):
    """Reads several files character by character and redirects their contents
    to `/dev/null`.

    """
    for filename in filenames:
        with open("/dev/null", "wb") as fp:
            for char in chars(filename, buffersize):
                fp.write(char)

if __name__ == "__main__":
    # Try reading several files varying the buffer size
    import sys
    buffersize = int(sys.argv[1])
    filenames  = sys.argv[2:]
    sys.exit(main(buffersize, filenames))

我建议的代码与您接受的答案基本相同：从文件中读取给定数量的字节。不同之处在于，它首先读取大量数据（对于X86，4006是一个很好的默认值，但您可能要尝试1024或8192；页面大小的任意倍数），然后在该数据块中生成字符一个。

对于大型文件，我提供的代码可能会更快。以托尔斯泰的《战争与和平》全文为例。这些是我的计时结果（使用OS X 10.7.4的Mac Book Pro； so.py是我为粘贴的代码指定的名称）：

$ time python so.py 1 2600.txt.utf-8
python so.py 1 2600.txt.utf-8  3.79s user 0.01s system 99% cpu 3.808 total
$ time python so.py 4096 2600.txt.utf-8
python so.py 4096 2600.txt.utf-8  1.31s user 0.01s system 99% cpu 1.318 total

现在：不要以缓冲区大小4096作为普遍真理；看看我得到的不同大小的结果（缓冲区大小（字节）与墙时间（秒））：

   2 2.726 
   4 1.948 
   8 1.693 
  16 1.534 
  32 1.525 
  64 1.398 
 128 1.432 
 256 1.377 
 512 1.347 
1024 1.442 
2048 1.316 
4096 1.318 

如您所见，您可以早一点开始看到收益（我的时间安排可能非常不准确）；缓冲区大小是性能和内存之间的权衡。默认值4096是一个合理的选择，但与往常一样，首先进行测量。

Python本身可以以交互方式为您提供帮助：

>>> help(file.read)
Help on method_descriptor:

read(...)
    read([size]) -> read at most size bytes, returned as a string.

    If the size argument is negative or omitted, read until EOF is reached.
    Notice that when in non-blocking mode, less data than what was requested
    may be returned, even if no size parameter was given.

只是：

myfile = open(filename)
onecaracter = myfile.read(1)

今天，我在观看Raymond Hettinger将代码转换为漂亮的，成语的Python时学到了一个新的用法：

import functools

with open(filename) as f:
    f_read_ch = functools.partial(f.read, 1)
    for ch in iter(f_read_ch, ''):
        print 'Read a character:', repr(ch) 

只需读一个字符

f.read(1)

您应该尝试f.read(1)，这绝对是正确的，也是正确的做法。

这也将起作用：

with open("filename") as fileObj:
    for line in fileObj:  
        for ch in line:
            print(ch)

它遍历文件中的每一行以及每一行中的每个字符。

f = open('hi.txt', 'w')
f.write('0123456789abcdef')
f.close()
f = open('hej.txt', 'r')
f.seek(12)
print f.read(1) # This will read just "c"

作为补充，如果您正在读取包含vvvvery巨大行的文件，这可能会破坏您的内存，则可以考虑将它们读入缓冲区，然后产生每个字符

def read_char(inputfile, buffersize=10240):
    with open(inputfile, 'r') as f:
        while True:
            buf = f.read(buffersize)
            if not buf:
                break
            for char in buf:
                yield char
        yield '' #handle the scene that the file is empty

if __name__ == "__main__":
    for word in read_char('./very_large_file.txt'):
        process(char)

#reading out the file at once in a list and then printing one-by-one
f=open('file.txt')
for i in list(f.read()):
    print(i)