Python 实现，读取文件行数，类似 wc -l 的功能，小文件无所谓，如果遇到大文件（5G），就要选择一种性能较高的方法了。

列出一下方法：

1. readline 读所有行

def readline_count(file_name):
    return len(open(file_name).readlines())

2. 依次读取文件每行内容进行计数

def simple_count(file_name):
    lines = 0
    for _ in open(file_name):
        lines += 1
    return lines

3. sum 计数

def sum_count(file_name):
    return sum(1 for _ in open(file_name))

4. enumerate 枚举计数

def enumerate_count(file_name):
    with open(file_name) as f:
        for count, _ in enumerate(f, 1):
            pass
    return count

5. buff count 每次读取固定大小,然后统计行数

def buff_count(file_name):
    with open(file_name, 'rb') as f:
        count = 0
        buf_size = 1024 * 1024
        buf = f.read(buf_size)
        while buf:
            count += buf.count(b'\n')
            buf = f.read(buf_size)
        return count

6. 调用使用 wc 命令计算行

def wc_count(file_name):
    import subprocess
    out = subprocess.getoutput("wc -l %s" % file_name)
    return int(out.split()[0])

7. 在buff_count基础上引入partial

def partial_count(file_name):
    from functools import partial
    buffer = 1024 * 1024
    with open(file_name) as f:
        return sum(x.count('\n') for x in iter(partial(f.read, buffer), ''))

8. iter count，在buff_count基础上引入itertools 模块

def iter_count(file_name):
    from itertools import (takewhile, repeat)
    buffer = 1024 * 1024
    with open(file_name) as f:
        buf_gen = takewhile(lambda x: x, (f.read(buffer) for _ in repeat(None)))
        return sum(buf.count('\n') for buf in buf_gen)