Python Tutorial 学习笔记5 --IO

There are two ways to format your output; the first way is to do all the string handling yourself; using string slicing and concatenation operations you can create any layout you can imagine. The string types have some methods that perform useful operations for padding strings to a given column width; these will be discussed shortly. The second way is to use the str.format() method.

One question remains, of course: how do you convert values to strings? Luckily, Python has ways to convert any value to a string: pass it to therepr() or str() functions. The str() function is meant to return representations of values which are fairly human-readable, while repr() is meant to generate representations which can be read by the interpreter.

例1：

例2：the str.rjust() method of string objects, which right-justifies a string in a field of a given width by padding it with spaces on the left.There are similar methods str.ljust() and str.center().

例3：There is another method, str.zfill(), which pads a numeric string on the left with zeros.

例4：The brackets and characters within them (called format fields) are replaced with the objects passed into the str.format() method. A number in the brackets refers to the position of the object passed into thestr.format() method.

例5：'!s' (apply str()) and '!r' (apply repr()) can be used to convert the value before it is formatted.

例6：Passing an integer after the ':' will cause that field to be a minimum number of characters wide. This is useful for making tables pretty.

NOTES：This could also be done by passing the table as keyword arguments with the ‘**’ notation.

例7：Old string formatting. The % operator can also be used for string formatting.

例8：open() returns a file object, and is most commonly used with two arguments:open(filename, mode).

例9：It is good practice to use the with keyword when dealing with file objects.It is also much shorter than writing equivalent try-finally blocks.

 

例10：data exchange with json

例11：If f is a file object opened for writing, we can use dumps() serializes the object to a file.