If condition judgment statement 21

One, Python's comparison operation

1. All Python objects support comparison operations

1) can be used to test the equality, relative size, etc.;

2) If it is a composite object, Python will check all its parts, including automatically traversing all levels of nested objects until the final result can be obtained;

2. Test operator

1) The equality of the test value of the "= =" operator;

2) "is" expression test object consistency;

For example:

In [1]: a=5 in [2]: b=6in [3]: a>bout[3]: falsein [4]: l1 ={' x ', ' y ', ' z '}in [5]: l2={' x ', ' y ', ' z '}in [6]: id (L1) out[6]: 39385440in [7]:  id (L2) out[7]: 39385672in [8]: l1 == l2out[8]: truein [9]: x  in l1                        //x is not quoted and is considered a variable ;---------------------------------------------------------------------------nameerror                                   Traceback  (Most recent call  last) <ipython-input-9-87d65672e822> in <module> ()----> 1 x in  l1NameError: name  ' x '  is not definedin [10]:  ' X '  in l1out[10]: true

Different types of comparison methods in 3.python

1) Number: compare by relative size;

2) String: Compare in dictionary order by character;

3) List and tuple: From left to right to compare the contents of each part;

4) Dictionary: Compare the list of (keys, values) after sorting;

4.python True and False

1) Any non-0 numeric and non-empty objects are true;

2) The number 0, the empty object and the special object none are false;

3) Comparisons and equivalence tests are applied recursively to the data structure;

4) The return value is true or false;

5. Combination condition test

1) x and Y: Logic and arithmetic;

2) x or Y: logic or operation;

3) x or Y: non-operational;

Second, if condition test syntax format

1.if Branch Syntax

If Boolean_expression1:suite1elif boolean_expression2:suite2...else:else_suite

The elif statement is optional;

Pass is used only for placeholders, and then when the related statements are filled;

2.if Combination Conditional syntax

A = X if Y else Z

If Y://If y is established, perform a=x.    If Y is not established, perform a=x. A = xelse a = Z

Example of 2.if condition judgment

Dual Branch in [14]: x = 5in [15]: y = 7in [16]: if x  > y:   ....:     print  "The max number is  %d. "  % x   ....: else:   ....:     print   "the max number is %d."  % y   ....:     the max number is 7.// Multi-branch in [17]: name =  "Jack" in [18]: if name ==  "Tom":    ....:     print  "It ' s %s."  % name   ....: elif name ==  "Mary":   ....:      print  "It ' s %s."  % name   ....: else:   ....:     print   "Alien."    ....:      alien.//Combination condition judgment In [25]: a = 7in [26]: b = 9in [27]: max  = a if a > b else bin [28]: print max9

        

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If condition judgment statement 21