Python 必须了解的5种高级特征

x = lambda a, b : a * b
print(x(5, 6)) # prints '30'

x = lambda a : a*3 + 3
print(x(3)) # prints '12'

def square_it_func(a):
 return a * a

x = map(square_it_func, [1, 4, 7])
print(x) # prints '[1, 16, 49]'

def multiplier_func(a, b):
 return a * b

x = map(multiplier_func, [1, 4, 7], [2, 5, 8])
print(x) # prints '[2, 20, 56]'看看上面的示例！我们可以将函数应用于单个或多个列表。实际上，你可以使用任何 Python 函数作为 map 函数的输入，只要它与你正在操作的序列元素是兼容的。

# Our numbers
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]

# Function that filters out all numbers which are odd
def filter_odd_numbers(num):

 if num % 2 == 0:
  return True
 else:
  return False

filtered_numbers = filter(filter_odd_numbers, numbers)

print(filtered_numbers)
# filtered_numbers = [2, 4, 6, 8, 10, 12, 14]

from itertools import *

# Easy joining of two lists into a list of tuples
for i in izip([1, 2, 3], ['a', 'b', 'c']):
 print i
# ('a', 1)
# ('b', 2)
# ('c', 3)

# The count() function returns an interator that 
# produces consecutive integers, forever. This 
# one is great for adding indices next to your list 
# elements for readability and convenience
for i in izip(count(1), ['Bob', 'Emily', 'Joe']):
 print i
# (1, 'Bob')
# (2, 'Emily')
# (3, 'Joe') 

# The dropwhile() function returns an iterator that returns 
# all the elements of the input which come after a certain 
# condition becomes false for the first time. 
def check_for_drop(x):
 print 'Checking: ', x
 return (x > 5)

for i in dropwhile(should_drop, [2, 4, 6, 8, 10, 12]):
 print 'Result: ', i

# Checking: 2
# Checking: 4
# Result: 6
# Result: 8
# Result: 10
# Result: 12


# The groupby() function is great for retrieving bunches
# of iterator elements which are the same or have similar 
# properties

a = sorted([1, 2, 1, 3, 2, 1, 2, 3, 4, 5])
for key, value in groupby(a):
 print(key, value), end=' ')

# (1, [1, 1, 1])
# (2, [2, 2, 2]) 
# (3, [3, 3]) 
# (4, [4]) 
# (5, [5]) 

# (1) Using a for loopv
numbers = list()

for i in range(1000):
 numbers.append(i+1)

total = sum(numbers)

# (2) Using a generator
 def generate_numbers(n):
  num, numbers = 1, []
  while num < n:
   numbers.append(num)
  num += 1
  return numbers
 total = sum(generate_numbers(1000))

 # (3) range() vs xrange()
 total = sum(range(1000 + 1))
 total = sum(xrange(1000 + 1))