Python learning notes (2) process control functions

Python Study Notes (2)

Process Control

If... else... elif

Example:

If 1> 2:

Print 'aaa'

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If 1> 2:

Print 'aaa'

Else:

Print 'bbbbbb'

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If 1> 2:

Print 'aaa'

Elif 1> 0:

Print 'bbbbbb'

Else:

Print 'cccccc'

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If 2> 1:

Print 'aaa'

Print 'bbbbbb'

Output: AAAA

BBBB

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If 2 <1:

Print 'aaa'

Print 'bbbbbb'

Output: BBBB

If indentation indicates the running range

Logical operators

And/or/not

For

For x in 'abcde ':

Print x

Output:

A

B

C

D

E

Range (start, stop [, step])Generation Sequence

Range (10) generates [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Range (5, 9) generates [5, 6, 7, 8]

Range (, 2) 2 is a step, generating [1, 3, 5, 7, 9]

Example:

For x in range (10 ):

Print x, 'aaa'

Output 10 times x + AAAA
In python, loops are different from those in C. You can also add elsefor x in range (5 ):
Print x
Else:
Print 'end'
Output end after output
For x in range (5 ):
Print x
If x> 2:
Break
Else:
Print 'end'

But in this way, the end will not output
Return break, continue, pass placeholder, code village

Convenient sequence and Dictionary

Convenience SequenceExample: a = ['A', 'B', 'C', 'D', 'D']
For x in range (len ()):
Print a [x]
Or for x in:
Print x

Convenient dictionary:A = {1: 'A', 2: 'B', 3: 'C', 4: 'D', 5: 'D '}
For x in:
Print x
Will output the dictionary key
For x in:
Print a [x]
Output value
For x, y in a. items ():
Print x, y
The sequence x that generates key-value pairs using items () is the key, and y is the value.

While

Example:

I = 0
While I <10:
Print I
I + = 1

Output 0 to 9
While can also be added with else
I = 0
While I <10:
Print I
I + = 1
Else:
Print 'end'
Output 0 ~ The end will be output after 9, and the else content from the break will not be executed.

Function

Function Definition

Define implementation a + B

Example:

Def add (a = 1, B = 2 ):

Return a + B

Print add ()

Output 5

You can define the default parameters.

Def add (a = 1, B = 2 ):

Print a + B

Add ()

Output 3

* And **

* Indicates a tuples or list.

** Indicates a dictionary.

Def add (a, B ):

Return a + B

T = (1, 2)

Print add (t)

This will cause errors

If you change to print add (* t), no error will occur.
If two more parameters are written in add (,), an error is defined as def add (a, B, * args): return a + B, args is a redundant parameter for storing tuples. Here args is (3, 4)
Def f (name = 'name', age = '0 '):
Print "name: % s, age: % s" % (name, age)
F (* ('wang', '18 '))
F (* ('18', 'wang '))
Output: name: wang, age: 18
Name: 18, age: wang


Def f (name = 'name', age = '0 '):
Print "name: % s, age: % s" % (name, age)
F (name = 'wang', age = '18 ')
F (age = 18, name = 'wang ')
Both f Functions output name: wang, age: 18 instead of name = 18, age = wang.
In this case, def f (name = 'name', age = '0 '):
Print "name: % s, age: % s" % (name, age)
A = {'age': '18', 'name': 'wang '}
F (**)

Name: wang, age: 18

Def f (name = 'name', age = '0', * args, ** kwargs ):
# Print "name: % s, age: % s" % (name, age)
Print kwargs
F (x = 'x', y = 'y ')

{'Y': 'y', 'x': 'X '}

Lambda expressions

Def add (x, y ):
Return x + y

G = lambda x, y: x + y # lambda expression, equivalent to add

Print add (1, 2)
Print g (1, 2)

Reduce

Implement factorial using reduce
Def f (x, y ):
Return x * y


L = range (1, 6)
Print reduce (f, l) # reduce takes 2 at a time