Python基础语法--一些例子
2017-06-02 17:51
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1.
2.range
3.strings
4.strings的不可变性
5.元组(同样具有不可变性)
6.set无序,不允许重复
7.字典:
8.input()
9.string format
10.
11.
12.覆盖方法:
>>> print(7//2) 3 >>> print(7/2) 3.5 >>> my_list=[1,2,3,4] >>> A=my_list*3 >>> A [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4] >>> my_list[2]=45 >>> A [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4] >>> my_list = [1,2,3,4] >>> A = [my_list]*3 >>> print(A) [[1, 2, 3, 4], [1, 2, 3, 4], [1, 2, 3, 4]] >>> my_list[2]=45 >>> print(A) [[1, 2, 45, 4], [1, 2, 45, 4], [1, 2, 45, 4]] >>> A=[1,2,3,4] >>> A.reverse() >>> A [4, 3, 2, 1] >>> (54).__add__(21) 75
2.range
>>> range(10) range(0, 10) >>> list(range(10)) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> range(5,10) range(5, 10) >>> list(range(5,10)) [5, 6, 7, 8, 9] >>> list(range(5,10,2)) [5, 7, 9] >>> list(range(10,1,-1)) [10, 9, 8, 7, 6, 5, 4, 3, 2]
3.strings
>>> "David" 'David' >>> my_name="David" >>> my_name[3] 'i' >>> my_name*2 'DavidDavid' >>> len(my_name) 5 >>> my_name 'David' >>> my_name.upper() 'DAVID' >>> my_name.center(10) ' David ' >>> my_name.find('v') 2 >>> my_name.split('v') ['Da', 'id']
4.strings的不可变性
>>> my_list [1, 3, True, 6.5] >>> my_list[0]=2**10 >>> my_list [1024, 3, True, 6.5] >>> my_name 'David' >>> my_name[0]='X' Traceback (most recent call last): File "<pyshell#84>", line 1, in <module> my_name[0]='X' TypeError: 'str' object does not support item assignment
5.元组(同样具有不可变性)
>>> my_tuple = (2,True,4.96) >>> my_tuple (2, True, 4.96) >>> len(my_tuple) 3
>>> my_tuple[0] 2 >>> my_tuple*3 (2, True, 4.96, 2, True, 4.96, 2, True, 4.96) >>> my_tuple[0:2] (2, True) >>> my_tuple[1]=False Traceback (most recent call last): File "<pyshell#44>", line 1, in <module> my_tuple[1]=False TypeError: 'tuple' object does not support item assignment
6.set无序,不允许重复
>>> {3.6,3.6,"cat",4.5,False} {3.6, False, 4.5, 'cat'} >>> my_set={3.6,3.6,"cat",4.5,False} >>> my_set {3.6, False, 4.5, 'cat'} >>> len(my_set) 4
>>> False in my_set True >>> "dog" in my_set False
>>> your_set={3.6,100,99} >>> my_set.union(your_set) {False, 99, 4.5, 100, 3.6, 'cat'} >>> my_set.intersection(your_set) {3.6} >>> my_set & your_set {3.6} >>> my_set.difference(your_set) {False, 4.5, 'cat'} >>> my_set - your_set {False, 4.5, 'cat'} >>> {3.6,100}.issubset(your_set) True >>> {3.6,100} <= your_set True >>> my_set.add("house") >>> my_set {False, 4.5, 3.6, 'house', 'cat'} >>> my_set.remove(4.5) >>> my_set {False, 3.6, 'house', 'cat'} >>> my_set.pop() False >>> my_set {3.6, 'house', 'cat'} >>> my_set.clear() >>> my_set set()
7.字典:
>>> capitals = {'Iowa':'DesMoines','Wisconsin':'Madison'} >>> capitals {'Iowa': 'DesMoines', 'Wisconsin': 'Madison'} >>> print(capitals['Iowa']) DesMoines >>> capitals['Utah']='SaltLakeCity' >>> print(capitals) {'Iowa': 'DesMoines', 'Wisconsin': 'Madison', 'Utah': 'SaltLakeCity'} >>> print(len(capitals)) 3 >>> for k in capitals: print(capitals[k]," is the captial of ",k) DesMoines is the captial of Iowa Madison is the captial of Wisconsin SaltLakeCity is the captial of Utah >>> del capitals['Utah'] >>> capitals {'Iowa': 'DesMoines', 'Wisconsin': 'Madison'}
>>> phone_ext={'david':1410, 'brad':1137} >>> phone_ext {'david': 1410, 'brad': 1137} >>> phone_ext.keys <built-in method keys of dict object at 0x03EA7C90> >>> phone_ext.keys() dict_keys(['david', 'brad']) >>> list(phone_ext.keys()) ['david', 'brad'] >>> "brad" in phone_ext True >>> 1137 in phone_ext False >>> phone_ext.values() dict_values([1410, 1137]) >>> list(phone_ext.values()) [1410, 1137] >>> phone_ext.items() dict_items([('david', 1410), ('brad', 1137)]) >>> list(phone_ext.items()) [('david', 1410), ('brad', 1137)] >>> phone_ext.get("brad") 1137 >>> phone_ext.get("kent") >>> phone_ext.get("kent","NO ENTRY") 'NO ENTRY' >>> del phone_ext >>> phone_ext Traceback (most recent call last): File "<pyshell#96>", line 1, in <module> phone_ext NameError: name 'phone_ext' is not defined >>> phone_ext={'david':1410, 'brad':1137} >>> del phone_ext["david"] >>> phone_ext {'brad': 1137}
8.input()
>>> user_name = input('Please enter your name: ') Please enter your name: ZXM >>> user_name 'ZXM'
user_radius = input("Please enter the radius of the circle ") radius = float(user_radius) diameter = 2 * radius
9.string format
>>> print("Hello","World", sep="***") Hello***World >>> print("Hello","World", end="***") Hello World*** >>> print("Hello", end="***"); print("World") Hello***World >>> name="zxm" >>> age=27 >>> print(name," is ",age," years old.") zxm is 27 years old. >>> print("%s is %d years old." %(name,age)) zxm is 27 years old. >>> price=24 >>> item="banana" >>> print("The %s cost %d cents." %(item,price)) The banana cost 24 cents. >>> print("The %+10s cost %5.2f cents." %(item,price)) The banana cost 24.00 cents. >>> item_dict={"item":"banana","cost:"24} SyntaxError: invalid syntax >>> item_dict={"item":"banana","cost":24} >>> print("The %(item)s costs %(cost)7.1f cents"%item_dict) The banana costs 24.0 cents >>> print("The %+10s cost %10.2f cents." %(item,price)) The banana cost 24.00 cents. >>> price=214455667 >>> print("The %+10s cost %10.2f cents." %(item,price)) The banana cost 214455667.00 cents.
10.
>>>[ch.upper() for ch in 'comprehension' if ch not in 'aeiou']
['C', 'M', 'P', 'R', 'H', 'N', 'S', 'N']
11.
>>> a_number = int(input("Please enter an integer ")) Please enter an integer -23
>>> import math >>> try: print(math.sqrt(a_number)) except: print("Bad Value for square root") print("Using absolute value instead") print(math.sqrt(abs(a_number))) Bad Value for square root Using absolute value instead 4.795831523312719 >>>
>>> if a_number < 0: raise RuntimeError("You can't use a negative number") else: print(math.sqrt(a_number)) Traceback (most recent call last): File "<pyshell#145>", line 2, in <module> raise RuntimeError("You can't use a negative number") RuntimeError: You can't use a negative number
12.覆盖方法:
class Fraction: def __init__(self,top,bottom): self.num = top self.den = bottom
def __str__ (self): return str(self.num) + "/" + str(self.den) >>> my_f = Fraction(3, 5) >>> print(my_f) 3/5 >>> print("I ate", my_f, "of the pizza") I ate 3/5 of the pizza >>> my_f.__str__()
'3/5' >>> str(my_f) '3/5'
def __add__(self, other_fraction): new_num = self.num*other_fraction.den + self.den*other_fraction.num new_den = self.den * other_fraction.den
return Fraction(new_num, new_den)
>>> f1 = Fraction(1, 4) >>> f2 = Fraction(1, 2) >>> f3 = f1 + f2 >>> print(f3) 6/8 >>>
def __eq__(self, other): first_num = self.num * other.den second_num = other.num * self.den return first_num == second_num
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