Python 基本语法
作者:互联网
- 加减乘除
x = 3
print(type(x)) # <class 'int'>
print(x, x + 1, x - 1, x * 2, x ** 2) # 3 4 2 6 9
x += 1
print(x) # 4
x *= 2
print(x) # 8
y = 2.5
print(type(y)) # <class 'float'>
print(y, y +1, y * 2, y ** 2) # 2.5 3.5 5.0 6.25
- 布尔
# Booleans
t = True
f = False
print(type(t)) # <class 'bool'>
print(t and f, t or f, not t, t != f, t == f) # False True False True False
- 字符串
hello = "hello"
world = "world"
hw = hello + world
hw12 = "%s %s %d" % (hello, world, 12)
print(hello, world, "!" ";", hw, ";", hw12) # hello world !; helloworld ; hello world 12
s = "helLo"
print(s.capitalize()) # Hello
print(s.upper()) # HELLO
print(s.lower()) # hello
print(s.rjust(7)) # __helLo
print(s.ljust(7)) # helLo__
print(s.center(7)) # _helLo_
print(s.replace("l",'(ell)')) # he(ell)Lo
print(' wo rld '.strip()) # wo rld
- 列表
xs = [3, 1, 2]
print(xs, xs[1], xs[-1]) # [3, 1, 2] 1 2
xs.append('bar')
print(xs) # [3, 1, 2, 'bar']
x = xs.pop()
print(x, xs) # bar [3, 1, 2]
- 切片
nums = list(range(5))
print(nums) # [0, 1, 2, 3, 4]
print(nums[-1]) # 4
print(nums[2:4]) # [2, 3]
print(nums[2:]) # [2, 3, 4]
print(nums[:2]) # [0, 1]
print(nums[:]) # [0, 1, 2, 3, 4]
print(nums[:-1]) # [0, 1, 2, 3]
nums[0:2] = [8, 9]
print(nums) # [8, 9, 2, 3, 4]
- 循环访问列表
animals = ['cat', 'dog', 'monkey']
for animal in animals:
print(animal)
cat
dog
monkey
for idx, animal in enumerate(animals):
print('%d:%s' % (idx + 1, animal))
1:cat
2:dog
3:monkey
nums = [0, 1, 2, 3, 4]
squares = []
for x in nums:
squares.append(x ** 2)
print(squares) # [0, 1, 4, 9, 16]
nums = [0, 1, 2, 3, 4]
squares = [x ** 3 for x in nums]
print(squares) # [0, 1, 8, 27, 64]
nums = [0, 1, 2, 3, 4]
squares = [x ** 3 for x in nums if x % 2 == 0]
print(squares) # [0, 8, 64]
- 字典
d = {'cat': 'cute', 'dog': 'furry'}
print(d['cat']) # cute
print('cat' in d) # True
d['fish'] = 'wet'
print(d) # {'fish': 'wet', 'cat': 'cute', 'dog': 'furry'}
print(d.get('fish', 'N/A')) # wet
print(d.get('fi sh', 'N/A')) # N/A
del d['fish']
print(d.get('fish', 'N/A')) # N/A
- 循环访问字典
d = {'person': 2, 'cat': 4, 'spider': 8}
for animal in d:
legs = d[animal]
print('A %s has %d legs' % (animal, legs))
A spider has 8 legs
A cat has 4 legs
A person has 2 legs
for animal, legs in d.items():
print('A %s has %d legs' % (animal, legs))
A cat has 4 legs
A person has 2 legs
A spider has 8 legs
nums = [0, 1, 2, 3, 4]
even_num_to_square = {x+1: x ** 2 for x in nums if x % 2 ==0}
print(even_num_to_square) # {1: 0, 3: 4, 5: 16}
- 集合
animals = {'dog', 'cat'}
animals.add('fish')
animals.remove('cat')
animals.add('dog') # does nothing and no return
print('dog' in animals) # True
print('do g' in animals) # False
print(len(animals)) # 3
animals = {'cat', 'dog', 'fish'}
for idx, animal in enumerate(animals):
print('#%d: %s' % (idx + 1, animal))
from math import sqrt
nums = {int(sqrt(x)) for x in range(30)}
print(nums) # {0, 1, 2, 3, 4, 5}
d = {(x, x + 1): x for x in range(3)}
t = (0, 1)
print(d) # {(0, 1): 0, (1, 2): 1, (2, 3): 2}
print(type(t)) # <class 'tuple'>
print(type(d[t])) # <class 'int'>
print(d[t]) # 0
print(d[(1, 2)]) # 1
- 函数
def sign(x):
if x > 0:
return 'positive'
elif x < 0:
return 'negative'
else:
return 'zero'
for x in [-1, 0, 1]:
print(sign(x))
negative
zero
positive
def hello(name, loud = False):
if loud:
print('HELLO,%s !' % name.upper())
else:
print('Hello,%s' % name)
hello('Bob') # Hello,Bob
hello('Fred', loud=True) # HELLO,FRED !
- 类
class Greeter(object):
def __init__(self, name):
self.name = name
def greet(self, loud=False):
if loud:
print('HELLO, %s!' % self.name.upper())
else:
print('Hello,%s' % self.name)
g = Greeter('Fred')
g.greet() # Hello,Fred
g.greet(loud=True) # HELLO, FRED!
标签:基本,animals,nums,Python,cat,语法,animal,print,legs 来源: https://www.cnblogs.com/yangzhaonan/p/10427360.html