import sys

with open("stream/test.txt") as f1:
 sys.stdout.write(f1.read()) # 默认情况下,read() 将读取字符,直至到达文件末尾
 sys.stdout.write(f1.read()) # 再次读取,将返回空字符串

print("---------------------")

with open("stream/test.txt", "r+") as f1:
 # read 的参数 size 是个整数,表示最多读取多少个字符
 sys.stdout.write(f1.read(3) + "\n")
 sys.stdout.write(f1.read()) # 读取剩下的字符

print("---------------------")

with open("stream/test.txt", "r+") as f1:
 # readline() 只读取到换行符(\n),而不是读到文件末尾
 sys.stdout.write(f1.readline())
 sys.stdout.write(f1.readline())

print("---------------------")

with open("stream/test.txt", "r+") as f1:
 # 一次性将文件的所有行读取为字符串列表
 lines = f1.readlines()
 for line in lines:
 sys.stdout.write(line)

print("---------------------")

with open("stream/test.txt", "r+") as f1:
 # readlines 的参数 hint 是个整数,限制读取的字符数量
 # 读取 hint 个字符后,会继续读取直到遇到换行符
 lines = f1.readlines(3)
 for line in lines:
 sys.stdout.write(line)

print("---------------------")

with open("stream/test.txt", "r+") as f1:
 # 流本身就是一个迭代器
 # 直接迭代流比先读取所有行再迭代更快,因为不需要在内存中保存所有行
 for line in f1:
 sys.stdout.write(line)

print("---------------------")

with open("stream/test.txt", "r+") as f1:
 f1.read(3)
 # tell()方法返回一个整数,表示从文件开头到当前流位置的字符数
 print(f1.tell()) # 3

 # seek() 方法用于移动文件读取指针
 # seek(0) 会将文件指针移动到文件开头
 f1.seek(0)
 print(f1.tell()) # 0
 sys.stdout.write(f1.readline())

 f1.seek(0, 2) # 移动到文件末尾
 print(f1.tell()) # 12