Python learning diary: day15: ------ built-in functions, pythonday15

Python learning diary: day15: ------ built-in functions, pythonday15

1. Scope-related

1) locals () --------- obtain the dictionary of local variables in the namespace in which the method is executed

# Return all names in the local scope

2) globals () -- get the dictionary of global variables

# Return all names in the global scope

2. String-Type Code Execution

Eval () executes the code of the string type and returns the result.

print(eval('1+2+3+4')

Exec () executes code of the string type

print(exec("1+2+3+4"))exec("print('hello,world')")

Compile Compilation

# Execcode1 = 'for I in range (): print (I)' compile1 = compile (code1, '', 'exec ') exec (compile1)

# Simple evaluate expression evalcode2 = '1 + 2 + 3 + 4' compile2 = compile (code2, '', 'eval') eval (compile2)

# Singlecode3 = 'name = input ("please input your name:") 'compile3 = compile (code3, '', 'single') name # The name variable does not exist before execution
Exec (compile3) # The interactive command is displayed during execution, prompting you to enter

3. iterator/generator correlation (3)

# Iterator. _ next __()
# Next (iterator)
# Iterator = iter (iteratable)
# Iterator = iteratable. _ iter __()

4. Input/Output
Input () input

S = input ("Enter the content:") # The input content is assigned to the s Variable print (s) # input and print. The data type is str.

Print () output source code parsing

Def print (self, * args, sep = '', end = '\ n', file = None ): # known special case of print "" print (value ,..., sep = '', end = '\ n', file = sys. stdout, flush = False) file: The default value is output to the screen. If it is set to a file handle, output to the file sep: The separator between multiple values is printed. The default value is space end: at the end of each print, the default line break is flush: Immediately output the content to the stream file, not cached """

5. Data Types:

Type (a) returns the Data type of variable.

6. Memory related:

Id (o) o is a parameter and returns the memory address of a variable.

Hash (o) o is a parameter and returns a hash value of the hash variable. If a non-hash variable is hashed, an error is returned.

# Hash-the hash values of the same hash data remain unchanged during a Program Execution
#-Dictionary addressing

T = (, 3) l = [, 3] print (hash (t) # hashprint (hash (l) # The '''result is: TypeError: unhashable type: 'list''' hash instance

7. File Operations

Open () open a file and return a file operator (file handle)

There are 6 file operation modes: r, w, a, r +, w +, and a +. Each mode can be operated in binary format (rb, wb, AB, rb +, wb +, AB +)

You can use encoding to specify the encoding.

8. Module operations

_ Import a module

9. Help

Help

Run help () on the console to enter the help mode. You can enter variable or variable type at will. Enter q to exit

You can also directly execute help (o) and o is a parameter to view the operations related to variable o...

# Differences between help and dir: (summarized by myself)

Dir () view the method name (not very detailed help) help view the method name and usage (more detailed help) 10,And call-related

Callable (o) and o are parameters. Check whether the variable is callable.

If o is a function name, True is returned.

 

Def func (): passprint (callable (func) # The parameter is the function name and can be called. Trueprint (callable (123) is returned. # The parameter is a number and cannot be called. False is returned.

11. Related to numbers

Number -- Data Type correlation: bool, int, float, complex

Number-hexadecimal conversion related: bin, oct, hex

Number-mathematical operations: abs, divmod, min, max, sum, round, pow # print (bin (10)-binary# Print (oct (10) -- octal

# Print (hex (10) -- hexadecimal
# Abs () returns the absolute value.
# Divmod () Division-> div division, mod Division
# Pow (2, 3)-> 2 ** 3 Power Calculation
# Pow (2, 3, 4) --> 2*3% 4, the last number is the remainder. Remainder after power operation
12, max

print(max([1,2,3,4]))print(max(1,2,3,4))print(max(1,2,3,-4))print(max(1,2,3,-4,key = abs))

13, min

print(min([1,2,3,4]))print(min(1,2,3,4))print(min(1,2,3,-4))print(min(1,2,3,-4,key = abs))