Python beginners Summary 3: files, collections, functions, variables, etc,

Python beginners Summary 3: files, collections, functions, variables, etc,

I. File Operations:

File Operation Process:

1. open the file, get the file handle, and assign it to a variable.

2. Operate the file through a handle

3. close the file

File opening modes include:

• R, read-only mode (default ).
• W, write-only mode. [Unreadable; created if no data exists; deleted if data exists ;]
• A. append mode. [Readable; created if it does not exist; appended content if it exists ;]

"+" Indicates that a file can be read and written simultaneously.

• R +, which can read and write files. [Readable; writable; appendable]
• W +, write and read
• A +, same as

"U" indicates that \ r \ n can be automatically converted to \ n (used in the same mode as r or r +) during read)

• RU
• R + U

"B" indicates processing binary files (for example, sending and uploading ISO image files via FTP, which can be ignored in linux and must be noted when processing binary files in windows)

• Rb
• Wb
• AB

 

Original file yesterday2:

 

 

(1) reading files

F = open ("yesterday2", 'R', encoding = "UTF-8") # file handle. 'R' is the Read mode. If it is not written, the default value is 'R ', 'W' is used to create a file, and the original file is gone.

Data2 = f. read ()

Print ('------ data2 ------ \ n', data2)

Execution result:

 

 

(2) for Loop File Reading

For I in range (3 ):
Print (f. readline () # Read one row each time and read three rows in total
For line in f. readlines ():
Print (line. strip () # strip () removes spaces and line breaks

The original file yesterday2 before running:

 

 

Execution result:

 

 

(3) Writing files

F = open ("yesterday2", 'w', encoding = "UTF-8 ")

F. write ("black heart \ n") # 'W' write creates a file, and the content of the original file is gone.
F. write ("why wocould you offer more \ n ")
F. write ("Why wocould you make it easier on me to satisfy ")

Execution result:

 

 

(4)

F = open ("yesterday2", 'R', encoding = "UTF-8 ")

Print (f. readlines () # each row is a list of elements ['black black heart \ n', 'Why wocould you offer more \ n ', 'Why wocould you make it easier on me to satisfy ']

(5)

F. readlines () is only suitable for reading small files, because the memory is fully read once loaded during reading.

So you can use a loop to read a row and delete a row, and save only one row in the memory to process large files:

Count = 0

F = open ("yesterday", 'R', encoding = "UTF-8 ")

For line in f:

If count = 4:

Print ('---------- I am a split line -------')

Count + = 1

Pass

Print (line. strip ())

Count + = 1

F. close ()

Execution result:

 

Figure (5)-1

NOTE: If "pass" in the above Code is rewritten to "continue", the execution result is as follows:

 

Figure (5)-2

Compared with figure (5)-1 and figure (5)-2, we found that the latter was missing: "If you call your friends and nobody's home. if you call a friend but no one is at home, this is because the execution mechanism of pass is different from that of continue. When count = 4 is set, the following print (line. strip (), and after continue, the program jumps to if count = 4:, so a row is printed less.

(6) read and write r +

F = open ("yesterday2", 'r + ', encoding = "UTF-8") # read/write

Print (f. readline ())

Print (f. readline ())

Print (f. readline ())

Print (f. tell ())

F. write ("\ n ------- add one line ----------- \ n") # At the end of the file

Print (f. readline ())

Execution result:

 

 

The original file becomes:

 

 

(7) binary file read rb

F = open ("yesterday2", 'rb') # Binary File Read

Print (f. readline ())

Print (f. readline ())

Print (f. readline ())

Execution result:

 

 

(8) modifying files

"Create a new file when modifying the file. The modified file appears in the new file """

F = open ("yesterday2", "r", encoding = "UTF-8 ")

F_new = open ("yesterday2.bak", "w", encoding = "UTF-8 ")

 

For line in f:

If "experienced a storm and endured loneliness" in line:

Line = line. replace ("the storm has endured the loneliness", "The storm has endured the loneliness ")

F_new.write (line)

F. close ()

F_new. close ()

After the execution, a new file yesterday2.bak is created:

 

 

(9) With statement: automatically close the file after execution

Syntax:

With open ("yesterday2", "r", encoding = "UTF-8") as f ,\

Open ("yesterday2", "r", encoding = "UTF-8") as f2:

Python specification: a single line of code should not exceed 80 characters, so you can use "\" to open multiple files and write multiple lines

2. progress bar Applet:

Import sys, time

For I in range (20 ):

Sys. stdout. write ("#")

Sys. stdout. flush ()

Time. sleep (0.1)

Iii. Set

List_1 = [1, 2, 5, 3, 2, 6, 4, 2, 6]

List_1 = set (list_1) # converts a list into a set, and the set is unordered and not repeated.

List_2 = set ([2, 5, 3, 22, 1])

 

Print (list_1, list_2) # {1, 2, 3, 4, 5, 6} {33, 2, 1, 5, 22}

Print (list_1, type (list_1) # {1, 2, 3, 4, 5, 6} <class 'set'>

 

# Intersection

Print (list_1. intersection (list_2) # = print (list_1 & list_2) # {1, 2, 5}

 

# Union

Print (list_1. union (list_2) # = print (list_1 | list_2) # {1, 2, 3, 4, 5, 6, 33, 22}

 

# Difference set

Print (list_1. difference (list_2) # = print (list_1-list_2) # {3, 4, 6}

 

# Subset

List_3 = set ([1, 2, 5])

Print (list_3. issubset (list_2) # True

 

# Symmetric difference set. The two sets are retrieved from each other.

Print (list_1. symmetric_difference (list_2) # = list_1 ^ list_2 # {33, 3, 4, 22, 6}

 

List_3 = set ([1, 2, 5])

List_4 = set ([4, 6, 8])

Print (list_3. isdisjoint (list_4) # returns True if there is no intersection between list_3 and list_4 # True

 

List_1. add (889) # add an item

List_1. update ([123,234,345]) # add multiple entries, = list_1. update ({123,234,345 })

Print (list_1) # {1, 2, 3, 4, 5, 6,345,234,889,123}

Iv. Local variables and global variables

Names = ["Lili", "Vae", "Cici"]

Def change_name ():

Names [0] = "Li" # list, set, and dictionary can be changed to global variables in the local area. (The tuples cannot be changed, and the strings and integers cannot be changed)

Print ("inside func", names)

Change_name ()

Print ("outside func", names)

Execution result:

Inside func ['lily', 'vae', 'cii']

Outside func ['lily', 'vae', 'cii']

V. Example of a Higher-Order Function

Def add (a, B, f ):

Return f (a) + f (B)

Res = add (3,-6, abs) # abs: Return the absolute value of the argument.

Print (res) #9

6. A Recursive example

Def calc (n ):

Print (n)

If int (n/2) = 0:

Return n

Return calc (int (n/2 ))

Calc (10) #10 5 2 1

VII,

1. functions and processes

# Functions

Def func1 ():

"Testing1, This is a function """

Print ('IN the func1 ')

Return 0

# A process is a function without return values.

Def func2 ():

'''Testing2, this is a process '''

Print ('IN the func2 ')

 

X = func1 () # output: in the func1

Y = func2 () # output: in the func1

 

Print ('from func1 return is % s' % x) # output from func1 return is 0

Print ('from func1 return is % s' % y) # output: from func1 return is None

2. function call

Import time

Def logger ():

Time_format = '% Y-% m-% d % x' # format: year, month, day, hour, minute, second

Time_current = time. strftime (time_format) # Convert a time tuple to a string according to a format specification.

With open('a.txt ', 'a +') as f:

F. write ('% s end action \ n' % time_current)

Def test1 ():

Print ('test1 starting action ...')

Logger ()

 

Test1 () # test1 starting action...

Create a new file a.txt at the same time:

 

 

3. function return value:

Def test1 ():

Print ('IN the test1 ')

 

Def test2 ():

Print ('IN the test2 ')

Return 0

 

Def test3 ():

Print ('IN the test3 ')

Return 1, 'Hello', ['bob', 'lili'], {'name': 'bob '}

 

Y = test2 ()

Z = test3 ()

Print (test1 () # None

Print (y) #0

Print (z) # (1, 'Hello', ['bob', 'lili'], {'name': 'bob'}) when return is more than one, return one tuples.

4. Default function parameters

# Default parameter features: When a function is called, default parameters are not required

Purpose: 1: def test (x, soft1 = True, soft2 = True). When the default installation value is set to True, soft1 is installed by default.

2: connect to the database: def conn (host, port = 3301)

Pass

Host default port number

(1)

Def test (x, y = 2 ):

Print (x)

Print (y)

Test (1, y = 3) #1 3

(2) parameter groups

1def test (* args ):

Print (args)

 

Test (,) # (1, 2, 3, 4, 5, 4) when the real parameters are not fixed, put the accepted real parameters into the tuples.

Test (* [1, 2, 3, 4, 5]) # (1, 2, 3, 4, 5) that is: args = tuple ([1, 2, 3, 4, 5])

2def test1 (x, * args ):

Print (x)

Print (args)

Test1 (, 7) #1)

3 # ** kwargs converts n keyword parameters into dictionaries. key: value, key: value...

Def test2 (** kwargs ):

Print (kwargs)

# Print (kwargs ['name'])

# Print (kwargs ['age'])

# Print (kwargs ['sex'])

 

Test2 (name = 'lili', age = 22, sex = 'y') # {'name': 'lili', 'age': 22, 'sex ': 'y '}

Test2 (** {'name': 'vae', 'age': 31, 'sex': 'y'}) # {'name': 'lili ', 'age': 22}

 

The output results are as follows:

A {'name': 'lili', 'age': 22, 'sex': 'y'} {'name': 'vae', 'age': 31, 'sex': 'y '}

Blili vae

C22 31

DY Y

Def test3 (name, ** kwargs ):

Print (name)

Print (kwargs)

Test3 ('cecila ', age = 22, sex = 'y ')

Output: cecila {'age': 22, 'sex': 'y '}

 

# * Args: receives N location parameters and converts them to a metagroup. ** kwargs receives keyword parameters and converts them to a dictionary.

Def test5 (name, age = 22, * args, ** kwargs ):

Print (name) # vae

Print (age) #31

Print (args) # output :()

Print (kwargs) # {'sex': 'y', 'hobby': 'book '}

Test5 ('vae', sex = 'y', holobby = 'book', age = 31)