Python anonymous functions, generators, built-in functions, derivation

Table of Contents

Day13: Built-in functions, generators and derivation

13.1 Anonymous functions

13.2 Generator

13.3 Built-in functions

13.4 Derivation

Day13: Built-in functions, generators and derivation

13.1 Anonymous function

An anonymous function is based on a lambda expression to define a function that can have no name. The format is: lambda parameter: function body

Due to restrictions, the function body can only write one line, so anonymous functions are suitable for simple business processing and can quickly and easily create functions

Parameters, supports any parameters.

lambda x: function body
lambda x1,x2: function body
lambda *args, **kwargs: function body

The function body can only support a single line of code.
```
def xxx(x):
    return x + 100
    
lambda x: x + 100
```
Return value, by default, the result of the execution of a single line of code in the function body is returned to the execution part of the function.
```
func = lambda x: x + 100
?
v1 = func(10)
print(v1) # 110
```

Supplementary expansion: ternary operations

Simple conditional statements can be implemented based on ternary operations, for example:

func = lambda x: "bigger" if x > 66 else "smaller"
?
v1 = func(1)
print(v1) # "Small"
?
v2 = func(100)
print(v2) # "Big"

Note: lambda expressions and ternary operations have nothing to do with each other and are two independent knowledge points.

13.2 Generator

The writing method created by the function + yield keyword can help us save memory under certain circumstances.
The characteristic is: the execution position in the function is recorded. The next time next is executed, it will continue to execute downwards from the previous position.

def func():
    print(111)
    yield 1
?
    print(222)
    yield 2
?
    print(333)
    yield 3
?
    print(444)
    #When return is encountered at the end or in the middle, the program explodes: StopIteration error
data = func()
?
# Execute the generator function func and return the generator object.
# Note: When the generator function is executed, the code inside the function will not be executed.
# Use the generator function normally and use a for loop (no error will be reported when it ends)
data = func()
?
for item in data:
    print(item)

Application scenario: When we need to create a lot of data in memory, we can think of using a generator to generate bit by bit (use a bit to produce a bit) to save memory overhead.

13.3 Built-in functions

Python provides us with many convenient built-in functions. Here we have compiled 36 for everyone to explain.

Group 1 (5 pieces)

abs, absolute value
```
v = abs(-10)
```

pow, index

v1 = pow(2,5) # 2 to the 5th power 2**5
print(v1)

sum, sum

v1 = sum([-11, 22, 33, 44, 55]) # Can be iterated - for loop
print(v1)

divmod, find quotient and remainder
```
v1, v2 = divmod(9, 2)
print(v1, v2)
```
round, n decimal places (rounded)
```
v1 = round(4.11786, 2)
print(v1) # 4.12
```

Group 2: (4 pieces)

min, minimum value

v1 = min(11, 2, 3, 4, 5, 56)
print(v1) #2
v2 = min([11, 22, 33, 44, 55]) # Type of iteration (for loop)
print(v2)
v3 = min([-11, 2, 33, 44, 55], key=lambda x: abs(x))
print(v3) # 2

max, maximum value

v1 = max(11, 2, 3, 4, 5, 56)
print(v1)
?
v2 = max([11, 22, 33, 44, 55])
print(v2)
v3 = max([-11, 22, 33, 44, 55], key=lambda x: x * 10)
print(v3) # 55

all, whether all are True
```
v1 = all( [11,22,44,""] ) # False
```
any, whether True exists
```
v2 = any([11,22,44,""]) # True
```

Group 3 (3 pieces)
- bin, decimal to binary
- oct, decimal to octal
- hex, decimal to hexadecimal
Group 4 (2 pieces)
- ord, obtains the unicode code point corresponding to the character (decimal)
```
v1 = ord("武")
print(v1, hex(v1))
```
- chr, get the corresponding character according to the code point (decimal)
```
v1 = chr(27494)
print(v1)
```
Group 5 (9 pieces)
- int
- foat
- str, unicode encoding
- bytes, utf-8, gbk encoding
```
v1 = "Big Shaobing" # str type
?
v2 = v1.encode('utf-8') # bytes type
?
v3 = bytes(v1,encoding="utf-8") # bytes type
```
- bool: Boolean type
- list: list
- dict: dictionary
- tuple: tuple
- set: collection

bool, list, tuple, dict, set, have been mentioned in the previous data types, click to jump to view

Group 6 (13)

len: length
print: output
input: input
open: open

type, get the data type

v1 = "123"
?
if type(v1) == str:
    pass
else:
    pass

range

for i in range(10):
    print(i)

# Output: 0 1 2 3 4 5 6 7 8 9

enumerate

v1 = ["Big Shaobing", "apple", 'root']
?
for num, value in enumerate(v1, 1):
    print(num, value)

id: memory address
hash
```
v1 = hash("Big Shaobing")
```
help, help information
- pycharm, no need
- terminal, use

zip

v1 = [11, 22, 33, 44, 55, 66]
v2 = [55, 66, 77, 88]
v3 = [10, 20, 30, 40, 50]
    
result = zip(v1, v2, v3)
for item in result:
    print(item)

callable, whether it is executable, and whether parentheses can be added after it.

v1 = "Big Shaobing"
v2 = lambda x: x
def v3():
    pass
?
?
print( callable(v1) ) # False
print(callable(v2))
print(callable(v3))

sorted, sorted

v1 = sorted([11,22,33,44,55])

info = {
    "wupeiqi": {
        'id': 10,
        'age': 119
    },
    "root": {
        'id': 20,
        'age': 29
    },
    "seven": {
        'id': 9,
        'age': 9
    },
    "admin": {
        'id': 11,
        'age': 139
    },
}
?
result = sorted(info.items(), key=lambda x: x[1]['id'])
print(result)

data_list = [
    '1-5 Compiler and Interpreter.mp4',
    '1-17 Today's homework.mp4',
    '1-9 Python interpreter type.mp4',
    '1-16 Today's summary.mp4',
    '1-2 Creation of Class Notes.mp4',
    '1-15 Pycharm usage and cracking (win system).mp4',
    '1-12 python interpreter installation (mac system).mp4',
    '1-13 python interpreter installation (win system).mp4',
    '1-8 Introduction to Python.mp4', '1-7 Classification of programming languages.mp4',
    '1-3 Common basic computer concepts.mp4',
    '1-14 Pycharm usage and cracking (mac system).mp4',
    '1-10 CPython interpreter version.mp4',
    '1-1 Today's summary.mp4',
    '1-6 Three essential things to learn about programming.mp4',
    '1-18 homework answers and explanations.mp4',
    '1-4 programming language.mp4',
    '1-11 Environment setup instructions.mp4'
]
result = sorted(data_list, key=lambda x: int(x.split(' ')[0].split("-")[-1]) )
print(result)

13.4 Derivation

Derivation is a very convenient function provided in Python, which allows us to create lists, dicts, tuples, and sets and initialize some values through one line of code.

Please create a list and initialize it with: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9…299 integer elements.

data = []
for i in range(300):
    data.append(i)

list

num_list = [ i for i in range(10)]
?
num_list = [[i,i] for i in range(10)]
?
num_list = [ [i,i] for i in range(10) if i > 6 ]

gather

num_set = { i for i in range(10)}
?
num_set = { (i,i,i) for i in range(10)}
?
num_set = { (i,i,i) for i in range(10) if i>3}

dictionary

num_dict = { i:i for i in range(10)}
?
num_dict = { i:(i,11) for i in range(10)}
?
num_dict = { i:(i,11) for i in range(10) if i>7}

Tuples, unlike other types.

# The inner loop will not be executed immediately to generate data, but a generator will be obtained.
data = (i for i in range(10))
print(data)
for item in data:
    print(item)

The knowledge points of the article match the official knowledge files, and you can further learn relevant knowledge. Python introductory skills treeBasic grammarCommonly used built-in functions 382,157 people are learning the system