Python Process Control

Python Process Control conditions
Summarize
Cycle
For loop
Script Simple to use
For typical 1+...+100python scripts
Small details of the sequence
Iterative traversal
Simple operation
Inline for Loop Classic-99 multiplication table
For loop
Common keywords
Guess random number
While
While compared to for
While loop
Ways to open a file
Ways to read files
Summary
Method for traversing a file
Summary:
Summarize
While loop
With+while Cycle
Summarize Python Process Control conditions

• If syntax

If expression:    # expression:    statement (s)    #  code block ELIF expression:    statement (s) Else exdpression:    Statement (s)

　　

• Score Judgment
  For example

[[email protected] day02]# cat 2.py #!/usr/bin/pythonscore = Int (raw_input ("Please input num:")) if score >=:    p Rint ' A '    print ' very good ' elif score >=:    print ' B '    print ' good ' elif score >=:    print ' C ' 
   print ' Pass ' else:    print ' Game over ' print ' END '

　　

• Operation
  Effect

[[email protected] day02]# python 2.py * input num:2game overend[[email protected] day02]# python 2.py please input Num:70cpassend[[email protected] day02]# python 2.py Please input num:89bgoodend[[email protected] day02]# python 2.py P Lease input Num:90avery Goodend

　　

• Uppercase and Lowercase methods
  For example

[email protected] day02]# cat 4.py #!/usr/bin/pythonyn = raw_input ("Please input [yes/no]:") yn = yn.lower ()    #用到一个字符串 Method: Uppercase replaces lowercase. The opposite is. Upperif yn = = ' y ' or yn = = ' yes ':    print ' programe is runing ... ' elif yn = ' n '  or yn = = ' no ':    print ' Progr Ame is exit ... "Else:    print" Please input [yes/no]: "

　　

• Operation
  Effect

[email protected] day02]# python 4.py please input [yes/no]: Yprograme is runing ... [email protected] day02]# python 4.py please input [yes/no]: Yesprograme is runing ... [email protected] day02]# python 4.py please input [yes/no]: Nprograme is exit ... [email protected] day02]# python 4.py please input [yes/no]: Noprograme is exit ... [email protected] day02]# python 4.py please input [yes/no]: aplease input [yes/no]:

　　

Summarize

除了shell之外，1返回的是正确，0返回的是错误。逻辑值（bool）包含了两个值：True：表示非空的量（比如：string,tuple,list,set,dictonary）,所有非零数。Fasle：表示0，None，空的量等。多条件判断可以用and，or 等

Cycle

• A loop is a structure that causes the program to repeat a certain number of times.
• The same is true for conditional loops, where the condition becomes false and the loop ends.

For loop

• For loop: In sequence, use for loop traversal.
• Grammar:

For Iterating_var in sequence:  statement (s)

　　

For example

In [4]: List1 = [1,2,3,4,5]in [5]: For i in List1:   ...:     print I ...    :     12345In [6]:  range (5) out[6]: [0, 1, 2 , 3, 4]in [7]: Range (0,10,2) out[7]: [0, 2, 4, 6, 8]in [8]: Range (0,10,3) out[8]: [0, 3, 6, 9]in [9]: For I in range: 
    ...:     print I ...   :     0123456789

　　

Script Simple to use

[[email protected] day02]# cat 5.py #!/usr/bin/pythonfor i in Range (1,11):    If I% 2 = = 0:        print i[[email protected ] day02]# vim 5.py[[email protected] day02]# python 5.py [2, 4, 6, 8, 10][[email protected] day02]# cat 5.py #!/usr/bin/py Thonprint [I for I in range (1,11) if I% 2 = = 0][[email protected] day02]# vim 5.py[[email protected] day02]# python 5.py [1, 9, 25, 49, 81] [[email protected] day02]# cat 5.py #!/usr/bin/pythonprint [i**2 for me in range (1,11) if I% 2! = 0]

　　

For typical 1+...+100python scripts

#!/usr/bin/pythonsum = 0for i in range (1,101):    sum = sum + i  # sum + = IPrint sum

　　

Small details of the sequence

range  占用内存xrange  遍历的时候才会占用内存推荐使用xrange

Iterative traversal

• Traversal sequence: Takes each element of the sequence out.
  -Directly from the sequence to take the value
  -use index to fetch values

Simple operation

• iterating through the dictionary
  for example

in [one]: Dict.fromkeys (' ABCDE ', +) #利用dict. Fromkeys method Create dictionary out[11]: {' A ': 100 , ' B ': +, ' C ': +, ' d ': +, ' e ': 100}in []: Dic1 = Dict.fromkeys (' abcde ', ') in []: dic1out[13]: {' A ': +, ' B ': 1 XX, ' C ': [+], ' d ': +, ' e ': 100}in []: for K in Dic1: #默认的情况下是取key ...: Print K ...-acbedin [+]: for K in              Dic1: #通过索引取出value ...: Print K, dic1[k] ...: A 100c 100b 100e 100d 100In []: for K in Dic1:  #也可以通过占位符, print out the desired effect ...: print "%s-to-%s"% (k, dic1[k]) ...: A--100c--100b--    100e-100d-100In [+]: for K in Dic1: ...: print "%s-to-%s"% (k, dic1[k]), #用, number can suppress line breaks      :---------------------and--------100In []: for K, V in Dic1.items ():p rint K, V #也可以通过itmes的方法取出key, Valuea 100c 100b 100e 100d 100In [+]: for K, V in Dic1.iteritems ():p rint K, VA 100c 100b 100e 10 0d 

　　

Inline for Loop Classic-99 multiplication table

• Operation

[[email protected] day02]# cat 7.py #!/usr/bin/pythonfor i in Xrange (1,10):                                      #乘法表不需要0, so value from 1 for    J in Xrange (1,i +1):                                 # (1,3) will be evaluated from 1, 2, excluding 3        print "%sx%s=%s"% (j, I, J*i),              #逗号抑制内部循环换行    print                                                           #内部循环结束进行换行输出 [[ Email protected] day02]# python 7.py1x1=11x2=2 2x2=41x3=3 2x3=6 3x3=91x4=4 2x4=8 3x4=12 4x4=161x5=5 2x5=10 3x5=15 4x5=20 5 x5=251x6=6 2x6=12 3x6=18 4x6=24 5x6=30 6x6=361x7=7 2x7=14 3x7=21 4x7=28 5x7=35 6x7=42 7x7=491x8=8 2x8=16 3x8=24 4x8=32 5x8 =40 6x8=48 7x8=56 8x8=641x9=9 2x9=18 3x9=27 4x9=36 5x9=45 6x9=54 7x9=63 8x9=72 9x9=81

　　

For loop

• For
• Else
• The For loop executes the Else statement if it ends normally.

Common keywords

Breakcontinueexitpass

　　

Operation
For example

[email protected] day02]# cat 8.py #!/usr/bin/pythonimport timeimport sysfor i in Xrange ():    if i = = 5:        continue    elif i = = 6:        Pass    elif i < 9:        time.sleep (1)        print i    elif i = = 9:        sys.exit (Ten) Else:        print "EMD" print "hahaha"

　　

Guess random number

[[email protected] day02]# cat 10.py #!/usr/bin/env pythonimport randomright = Random.randint (1,20) Count = 0while count &L T 6:    num = input (' Please input a number: ')    if num = = Right:print ' is Right ' break    else:if num > right: Print "Binger than right" else:print "Samller than right"    count + = 1

　　

Whilewhile compared to for

• The For loop is used on a number of cycles.

• The while loop is used for conditional control.

  While loop
• While loop, until the expression becomes false, the while loop is rolled out, and the expression is a logical expression and must return a true or false.
• Grammar

while expression:    statement(s)

# # operation
Example 1

[[email protected] day02]# cat 11.py #!/usr/bin/pythonn = 0while True:    if n = = Ten: Break    print  n, ' hello '    n + = 1

　　

Output

[[email protected] day02]# python 11.py 0 hello1 hello2 hello3 hello4 hello5 hello6 hello7 hello8 hello9 Hello

　　

Example 2

[[email protected] day02]# cat 12.py #!/usr/bin/pythonwhile True:   string = raw_input (' Please input string: ')   I F string = = "Q": Break        

　　

Output

[email protected] day02]# python 12.py please input string:eplease input string:wplease input string:q

　　

Example 3

[[email protected] day02]# cat 13.py #!/usr/bin/pythonx = ' while x! = ' Q ':    x = raw_input (' Please input: ')

　　

Output

[email protected] day02]# python 13.py please input:eplease input:wplease input:q

　　

Ways to open a file

R: Open in read mode
W: Open in write mode
A: Open in Append mode
r+: Open in read-write mode
w+: Open in read-write mode
A +: Open in read/write mode
RB: Open in binary read mode
WB: Open in binary write mode
AB: Open in binary append mode
rb+: Open in binary read/write mode
wb+: Open in binary read/write mode
ab+: Open in binary read/write mode

• Attention
  Opening a file with W overwrites the original file

Ways to read files

in [+]: FD.              Fd.close fd.errors fd.isatty fd.newlines fd.readinto fd.seek fd.truncate fd.xreadlines                                 fd.closed Fd.fileno fd.mode fd.next fd.readline fd.softspace fd.write Fd.encoding fd.flush fd.name fd.read fd.readlines Fd.tell fd.writelines in [ []: FD = open ('/tmp/tmp.txt ') in [to]: Fd.read () out[31]: ' 1\n2\n3\n ' in [+]: FD = open ('/tmp/tmp.txt ') in []: Fd.readline () out[33]: ' 1\n ' in [the]: Fd.readline () out[34]: ' 2\n ' in [+]: Fd.readline () out[35]: ' 3\n ' in [approx]: Fd.readline () out[36]: ' ' In [PNS]: FD = open ('/tmp/tmp.txt ') in []: Fd.readlines () out[38]: [' 1\n ', ' 2\n ', ' 3\n ']in [all]: Fd.readlines () out[39]: [] In [max]: FD = open ('/tmp/tmp.txt ') in [Max]: Fd.next () out[41]: ' 1\n ' in [[]: Fd.next () out[42]: ' 2\n ' in []: Fd.next () out[43 ]: ' 3\n ' in []: Fd.next ()---------------------------------------------------------------------------         Stopiteration                    Traceback (most recent) <ipython-input-44-3df4eef70a28> in <module> ()----> 1 F D.next ()

　　

Summary

fd.read()：返回的是字符串fd.readline()：返回的是每一行字符串fd.readlines()：返回的是一行列表

Method for traversing a file

[[email protected] day02]# Cat/tmp/tmp.txt123[[email protected] day02]# cat 14.py #!/usr/bin/pythonfd = open ('/tmp/tmp.t XT ') for line in Fd.readlines ():    print line,[[email protected] day02]# python 14.py 123[[email protected] day02]# Cat 1 4.py > 15.py[[email protected] day02]# vi 15.py [[email protected] day02]# cat 15.py #!/usr/bin/pythonfd = open ('/tmp/t Mp.txt ') for line in FD:    print line,[[email protected] day02]# python 15.py 123

　　

Summary:

print line后面加个逗号，可以抑制print默认的换行。for line in fd.readlines(): 这种方法会全部加在到内存中，不建议使用for line in fd: 这种方法类似于fd.next()，没循环一次加在一行，推荐使用。

Summarize

打开文件的时候要使用w方法会覆盖原来的文件，谨慎使用read(),readline()readlins()的区别是字符串和列表使用方法的时候选择最小消耗资源的方式

While loop

[[email protected] day02]# cat 16.py #!/usr/bin/pythonfd = open ('/tmp/tmp.txt ') while True: line     = Fd.readline ()    If not line:        break     print Line,fd.close[[email protected] day02]# python 16.py 123

　　

With+while Cycle

[[email protected] day02]# cat 17.py #!/usr/bin/pythonwith Open ('/tmp/tmp.txt ') as FD: While    True: line         = Fd.read Line ()        if is line:            break         print Line,[[email protected] day02]# python 17.py123

　　

Summarize

for循环有一定的次数while循环需要给出条件，条件语句后面要加:for和while遍历完文件之后需要加fd.close关闭文件，养成好习惯，如果不加python执行完系统也会进行回收with+while进行循环就不用加close的方法

Python Process Control