"0" python core programming, chapter II

1. The print statement also supports redirecting input to a file, as an example:

1 logfile = open ('/tmp/mylog.txt'a')  2print'Fatal error:invalid input! ' 3 logfile.close ()

2. Use logical operators to concatenate arbitrary expressions together and get a Boolean value:

1  and 2 = = 42False3or 2 < 44True5not 6.2 <= 66true7 >>> 3 < 4 < 58 True

The last example is often illegal in other languages, but Python supports expressions that are both concise and
Beautiful. It is actually an abbreviation for the following expression:

 and 4 < 5

3, Python does not support the C language of the self-increment 1 and the decrement 1 operator, because the + and-is also a single-mesh operator, Python will interpret--n as-(-N) to get N, the same ++n result is n. 4. Cyclic indexes and elements at the same time, enumerate (), Example:

1  for inch Enumerate (foo): 2 Print ' (%d) ' % i3 ... 4 A (0) 5 B (1)6 C (2)

5, List Resolution: You can use a for loop in a row to put all the values in a list

1>>> squared = [x * * 2 forXinchRange (4)]2>>> forIinchSquared:3...PrintI4 05164798 list parsing can even do more complex things, such as picking up the values that fit the requirements into the list:9>>> Sqdevens = [x * * 2 forXinchRange (8)if  notX% 2]Ten>>> One>>> forIinchSqdevens: A...PrintI - 0 -4 the16 -36

6. What is a property

Properties are data-related items, which can be simple data values or executable objects, such as functions and methods. Which objects have properties? A lot. Classes, modules, files and complex numbers, and so on, have properties. How do I Access object properties? Use the period property to identify the method. This means adding a period between the object name and the property name: Object.attribute

7. Table 2.1 useful built-in functions for new Python programmers

Function	Describe
Dir ([obj])	Displays the properties of the object and displays the name of the global variable if no argument is supplied
Help ([obj])	Displays the document string of an object in a neat and beautiful form, if no parameters are provided , the interactive help will be entered.
int (obj)	Convert an object to an integer
Len (obj)	Returns the length of an object
Open (FN, mode)	Open a file named fn in mode (' r ' = Read, ' W ' = Write)
Range ([[Start,]stop[,step])	Returns a list of integers. The starting value is start and the ending value is stop-1; Start The default value is 0, and the step default is 1.
Raw_input (str)	Waits for the user to enter a string that can provide an optional parameter str as a cue letter Interest.
STR (obj)	Convert an object to a string
Type (obj)	Returns the type of the object (the return value itself is a type Object!) ）

"0" python core programming, chapter II