010: 简单的文件读写

这里只是学习非常简单的文件读写，只是做一个简单的了解。

1. 内建方法open的定义：open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)

2. Open file and return a corresponding file object. If the file cannot be opened, an OSError is raised.

3. mode of 'r' : open for reading (default)

fr = open('example.txt', 'r')
text = fr.read()
fr.close()
print(text)

4. mode of 'w': open for writing, truncating the file first

fw = open('example.txt', 'w')
fw.write('hello!\n')
fw.write('this is a first file created by python!\n')
fw.close()