Python beginners must master 25 built in functions in detail

Directory input () print () set () str () chr (i) ord () bool () int () oct () hex () divmod () round () pow (x, y [, z]) sum (iterable) min (x, y, z, …) list () tuple () dict () len () reversed () enumerate () 33EN) Summary

input()

Function: Let the user input a string of characters from the console, press Enter to end the input and return the string

Note: Many beginners think it can return numbers, but it is wrong!

>>> line = input(" Input 1 Numbers: ")
 Input 1 Numbers: 1
>>> line
'1'  # <--  See clearly, this is not a number, just a string 

#  If you add directly... 
>>> line + 1   
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can only concatenate str (not "int") to str

#  The correct way is to put  line  Convert to numbers 
>>> int(line) + 1
2

print()

Function: Convert the parameters into strings and output them to the console

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

set()

Function: Construct the collection. A common method is to pass the list into set (), and then turn it into a list to realize the rearrangement of the list.

>>> set([1, 2, 3, 3])
{1, 2, 3}
#  In this way, the weight discharge is realized 
>>> list(set([1, 2, 3, 3]))
[1, 2, 3]

str()

Function: Converts an object to a string. Commonly used for splicing strings and numbers.

For example, this will report an error:

>>> 'My Score is: ' + 100
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can only concatenate str (not "int") to str

So use str to convert 1:

>>> 'My Score is: ' + str(100)
'My Score is: 100'

chr(i)

Function: Returns the characters corresponding to the integer i, which is often used to generate alphabets.

>>> chr(20013)
' Medium '
>>> chr(97)
'a'
#  And  ord()  Match to generate an alphabet 
>>> [chr(ord('a') + i) for i in range(26)]
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

ord()

Function: Returns the corresponding decimal value of characters in the encoding table

>>> ord(' Medium ')
20013
>>> ord('a')
97
#  And  chr()  Match to generate an alphabet 
>>> [chr(ord('a') + i) for i in range(26)]
['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']

bool()

Function: Judge the Boolean value of 1 object and return True or False

bool(1) => True
bool(0) => False
bool([]) => False

This function is rarely used in the actual project, just as a test tool, so that beginners can understand the Boolean state of each object.

int()

Function: Converts any binary string into an integer.

int('2') => 2
int('1010', 2) => 10  # 2 Binary system 1010 Convert to an integer 10

Description: Pass in the second parameter to specify the binary type of parameter 1.

bin()

Function: Converts an integer to a binary string

bin(2) => '0b10'
bin(10) => '0b1010'

Explanation: Why is there a 0b in front of the string? Because this is the standard way of writing, the number that begins with 0b for the next number is binary.

oct()

Function: Converts a decimal to octal string

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

0

hex()

Function: Converts a string from decimal to hexadecimal

>>> hex(11)
'0xb'
>>> hex(16)
'0x10'

abs()

Function: Take absolute value

>>> abs(-1)
1

divmod()

Function: Returns the quotient and remainder in the division operation at the same time, which is equivalent to one operation, and obtains the results of a//b and a% b at the same time.

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

3

round()

Function: 4 rounding and 5 inputting for 1 floating point number

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

4

pow(x, y[, z])

Function: If only x and y parameters are filled in, the y power of x is returned. If the z parameter is filled in, the module is taken again, which is equivalent to pow (x, y)% z.

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

5

sum(iterable)

Function: Sums all elements of the array iterable.

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

6

min (x, y, z, …)

Function: Returns the minimum number of all parameters

>>> min(1, 2, 3)
1
#  Incoming arrays can also 
>>> min([1, 2, 3])
1

max (x, y, z, …)

Function: Similar to min (), returns the maximum number of all parameters

list()

Function: When the passed parameter is empty, create a list; Convert the parameter to a list when the passed parameter is not empty

>>> list()
[]
#  When not empty 
>>> list('hello world')
['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']
#  Try passing into the dictionary 
>>> list({'a': 1, 'b': 2})
['a', 'b']

tuple()

Function: It is almost like list, except that list returns an array and tuple returns a tuple.

dict()

Function: Construct a dictionary

>>> print("hello", "world")
hello world
#  Many people don't know that other characters can be inserted between parameters 
>>> print("hello", "world", sep="~")
hello~world
#  You can even let each parameter occupy 1 Row 
>>> print("hello", "world", sep="\n")
hello
world

9

len()

Function: Returns the length of the object, or the number of elements

>>> len([1, 2])
2
>>> len({'a': 1, 'b': 2})
2
>>> len('hello')
5

reversed()

Function: Reverse the list.

Note: The return is not a list, but an iterator.

>>> reversed([1, 2, 3])
<list_reverseiterator object at 0x1016190a0>
#  Need to be converted to  list
>>> list(reversed([1, 2, 3]))
[3, 2, 1]
#  String also 1 Sample 
>>> reversed('abc')
<reversed object at 0x1015ffd90>
>>> list(reversed('abc'))
['c', 'b', 'a']

enumerate()

Function: Used for traversing objects, normal traversal, such as for el in array, can only get elements, can not get subscripts, with enumerate ().

>>> for i, el in enumerate('abc'):
...     print(i, el)
...
0 a
1 b
2 c

How to use this subscript? For example, it can be used to modify the elements in the array in reverse:

>>> alphabet = ['a', 'b', 'c']
>>> for i, el in enumerate(alphabet):
...     alphabet[i] = el.upper()
...
>>> alphabet
['A', 'B', 'C']

filter(func, iterable)

Function: Filter and return eligible elements

Note: 1 iterator is returned.

>>> alphabet = ['a', 'b', 'c', 'E', 'F', 'G']
>>> filter(lambda e: e.isupper(), alphabet)
<filter object at 0x1016190a0>
>>> list(filter(lambda e: e.isupper(), alphabet))
['E', 'F', 'G']

Summarize

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