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's wrong!
>>> line = input("Enter a number:") Enter a number: 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 method is to convert line into number first >>> int(line) + 1 2
print()
Function: after converting parameters into strings, 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 one line >>> print("hello", "world", sep="\n") hello world
set()
Function: construct a collection. A common method is to pass the list into set() and then turn it into a list to eliminate the duplication of the list.
>>> set([1, 2, 3, 3]) # This enables weight removal >>> list(set([1, 2, 3, 3])) [1, 2, 3]
str()
Function: converts an object into a string. It is often used to splice strings and numbers.
For example, an error will be reported:
>>> '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:
>>> 'My Score is: ' + str(100) 'My Score is: 100'
chr(i)
Function: returns the character corresponding to the integer i, which is often used to generate the alphabet.
>>> chr(20013) 'in' >>> chr(97) 'a' # Cooperate with ord() to generate the 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 decimal value corresponding to the character in the coding table
>>> ord('in') 20013 >>> ord('a') 97 # Cooperate with chr() to generate the 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 an object and return True or False
bool(1) => True bool(0) => False bool([]) => False
Note: this function is rarely used in actual projects. It is only used as a test tool to let beginners understand the Boolean state of each object.
int()
Function: convert any binary string into an integer.
int('2') => 2 int('1010', 2) => 10 # Binary 1010 to integer 10
Description: pass in the second parameter to specify the hexadecimal type of parameter 1.
bin()
Function: convert integer to binary string
bin(2) => '0b10' bin(10) => '0b1010'
Note: why is there a 0b in front of the string? Because this is the standard way of writing, starting with 0b means that the next number is binary.
oct()
Function: convert hexadecimal to octal string
oct(7) => '0o7' oct(8) => '0o10'
hex()
Function: convert decimal to hexadecimal string
>>> hex(11) '0xb' >>> hex(16) '0x10'
abs()
Function: take absolute value
>>> abs(-1) 1
divmod()
Function: return the quotient and remainder in the division operation at the same time, which is equivalent to one operation and get the results of a//b and a% b at the same time.
>>> divmod(1, 2) (0, 1) >>> divmod(4, 3) (1, 1)
round()
Function: rounds a floating-point number
>>> round(1.3333) 1 >>> round(1.3333, 2) # 2 means to keep 2 decimal places 1.33
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, take the module again, which is equivalent to pow (x, y)% z.
>>> pow(10, 2) 100 # amount to >>> 10**2 100 >>> pow(10, 2, 3) 1 # amount to >>> 10**2 % 3 1
sum(iterable)
Function: sum all elements of array iterable.
>>> sum([1, 2, 3]) 6
min(x, y, z, ...)
Function: returns the minimum number of all parameters
>>> min(1, 2, 3) 1 # You can also pass in an array >>> min([1, 2, 3]) 1
max(x, y, z, ...)
Function: similar to min(), return the maximum number of all parameters
list()
Function: create a list when the incoming parameter is empty; When the incoming parameter is not empty, the parameter is converted to a list
>>> list() [] # When not empty >>> list('hello world') ['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd'] # Try importing the dictionary >>> list({'a': 1, 'b': 2}) ['a', 'b']
tuple()
Function: almost as like as two peas, list, but list returns an array, and tuple returns tuples.
dict()
Function: construct dictionary
# Method 1: >>> dict(a=1, b=2) {'a': 1, 'b': 2} # Method 2: >>> dict(zip(['a', 'b'], [1, 2])) {'a': 1, 'b': 2} # Method 3: >>> dict([('a', 1), ('b', 2)]) {'a': 1, 'b': 2}
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: invert the list.
Note: the returned is not a list, but an iterator.
>>> reversed([1, 2, 3]) <list_reverseiterator object at 0x1016190a0> # Need to convert to list >>> list(reversed([1, 2, 3])) [3, 2, 1] # The same is true for strings >>> reversed('abc') <reversed object at 0x1015ffd90> >>> list(reversed('abc')) ['c', 'b', 'a']
enumerate()
Function: used to traverse objects. In normal traversal, such as for el in array, you can only get elements, not subscripts. You can use enumerate().
>>> for i, el in enumerate('abc'): ... print(i, el) ... 0 a 1 b 2 c
How does this subscript work? 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 qualified elements
Note: an 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']