myfile = open('file.txt', 'w+') #open file
myfile.write("this is my test")
myfile.close()
以“写”的方式打开文件，执行结果是this is my test被写入文件。如果不close，在第一次运行的时候，没有写成功，第二次才成功
=========================================================
myfile = open('file.txt', 'r') #open file
for line in myfile:
print(line)
myfile.close()
以“读”的方式打开文件，把文件中的内容一行一行打印出来,执行结果不太好，多出空白行：
this is my test
second
third
=========================================================
myfile = open('file.txt', 'r') #open file
yy = myfile.read()
print (yy)
myfile.close()
以“读”的方式打开文件，把文件内容全部读取出来，执行结果：
this is my test
second
third
==========================================================
myfile = open('file.txt', 'w+') #open file，
for line in myfile:
print(line)
myfile.close()
本来是想看看“w”和“w+”有什么不一样的，发现执行结果是file.txt里原本的内容被清空了，屏幕上也没打印什么，原来单执行myfile = open('file.txt', 'w+') 的时候，有清空文件的功效
如果把“w+”改为“w”，就提示出错：
Traceback (most recent call last):
File "C:\Python30\open file.py", line 11, in <module>
for line in myfile:
File "C:\Python30\lib\io.py", line 1739, in __next__
line = self.readline()
File "C:\Python30\lib\io.py", line 1813, in readline
while self._read_chunk():
File "C:\Python30\lib\io.py", line 1560, in _read_chunk
input_chunk = self.buffer.read1(self._CHUNK_SIZE)
AttributeError: 'BufferedWriter' object has no attribute 'read1'
===========================================================
myfile = open('file.txt', 'w+') #open file
myfile.write("this is my test")
for line in myfile:
print(line)
myfile.close()
执行结果：
文件写入正确，但是屏幕上没有任何输出，怀疑是因为写文件之后，指针是在文件的末尾，于是有以下这段：
myfile = open('file.txt', 'w+') #open file
myfile.write("this is my test")
myfile.seek(0)
for line in myfile:
print(line)
myfile.close()
运行结果全都正确，在文本里再加一行呢？
myfile = open('file.txt', 'w+') #open file
myfile.write("this is my test\nsecond\nthird")
myfile.seek(0)
for line in myfile:
print(line)
myfile.close()
运行结果：写入正确，输出多了两空白行：（原因是当执行print时，它会另起一行，而被打印的对象里已经包含一次回车）
this is my test
second
third
于是再修改:
myfile = open('file.txt', 'w+') #open file
myfile.write("this is my test\nsecond\nthird")
myfile.seek(0)
for line in myfile:
print(line.strip("\r\n"))
myfile.close()
运行结果正确：
this is my test
second
third
在此附上相关信息：
seek(offset[,whence])
Move to new file position. Argumentoffsetis a byte count. Optional argumentwhencedefaults toos.SEEK_SETor0(offset from start of file; offset should be>=0); other values areos.SEEK_CURor1(move relative to current position; offset can be positive or negative), andos.SEEK_ENDor2(move relative to end of file; offset is usually negative, although many platforms allow seeking beyond the end of a file).
offset为偏移量，whence默认为0，表示文件的开头；为1，表示当前问位置；为2表示文件的末尾
offset(1,0)：从开头向右跳一位
offset(1,1)：从当前位置向右跳一位
offset(-1,1)：从当前位置向左跳一位
offset(-1,2)：从末尾像左跳一位
str.strip([chars])
Return a copy of the string with the leading and trailing characters removed. Thecharsargument is a string specifying the set of characters to be removed. If omitted orNone, thecharsargument defaults to removing whitespace. Thecharsargument is not a prefix or suffix; rather, all combinations of its values are stripped:
>>>' spacious '.strip()'spacious'>>>'www.example.com'.strip('cmowz.')'example'===========================================================
myfile = open('file.txt', 'w+') #open file
myfile.write("this is my test")
print(myfile)
myfile.close()
执行结果：
文件写入正确，屏幕上输出： <io.TextIOWrapper object at 0x0222E470>
这个太傻了，应该不能直接就输出一个文本吧
