Python Process Control

Condition test:

An If condition test expression

Different types of comparisons: numbers: Comparing sizes

String: Per-character comparison by ASCII code table

Lists and tuples: Comparing the contents of each part from left to right

Dictionaries: Comparing sorted (key, value) lists

True and False in Python:

1, non-0 numbers and non-empty objects are true

2, number 0, empty object and none is False

3. Comparisons and equivalence tests are applied recursively to data structures

4, the return value is TRUE or False

Combination condition test:

X and y, x or y, not X

If syntax structure

If Boolean_expression1:

Suite1//Indent 4 characters

A = X If Y else Z:

If Y:

A = X

Else

A = Z

expression1 If boolean_expression else expression2

While and for loops

While loops are used to write common iteration structures

A For loop is a generic sequence iterator

Python Stealth Iteration Tool:

In member relationship testing; list parsing; map, reduce, filter functions

While Boolean_expression:

While_suite

Else

Else_suite

Else optional, boolean_expression end loop When the result is false, execute else.

Print x, which can be displayed on a single line in a non-wrapped line

Break: Jump out of the inner loop

Continue: advance to the next cycle and move to the beginning of the nearest layer loop.

ELSE code block: The loop terminates normally and else will not execute if the loop termination is caused by a break.

Range generates a sequence directly in memory before the for loop starts. Xrange is a data element that is generated at a time, one out, and can save memory resources.

The For loop executes faster than while.

Zip: Returns a list of tuples of parallel elements, often traversing several sequences in a for loop.

L1 = [1,2,3,4,5,6]

L2 = [' A ', ' B ', ' C ', ' d ', ' e ', ' F ']

Zip (L1,L2)

[(1, ' a '), (2, ' B '), (3, ' C '), (4, ' d '), (5, ' E '), (6, ' F ')]

Zip is used to construct the dictionary dynamically:

D = {}
for (k,v) in Zip (L1,L2):d [k] = V
D
{1: ' A ', 2: ' B ', 3: ' C ', 4: ' d ', 5: ' E ', 6: ' F '}

Python Process Control