数分でスタートPython
15511 ワード
取得コード:learnpython.py
PythonはGuido Van Rossumが1991年に創造した.現在存在する最も流行している言語の一つです.Pythonが好きになったのは、簡潔な文法のためです.基本的には擬似コードで実行されます.
注意:この文章はPython 2.7に適用されますが、Python 2に適用される可能性があります.x.Python 2.7は2020年にサポートを停止します.
書いたPythonコードは、Python 2.7と3に互換性がある.xは完全に可能である.Pythonの__を使うことでfuture__imports.Python 3で書かれたコードをPython 2で実行することができます.
詳細はこちらをご覧ください
PythonはGuido Van Rossumが1991年に創造した.現在存在する最も流行している言語の一つです.Pythonが好きになったのは、簡潔な文法のためです.基本的には擬似コードで実行されます.
注意:この文章はPython 2.7に適用されますが、Python 2に適用される可能性があります.x.Python 2.7は2020年にサポートを停止します.
書いたPythonコードは、Python 2.7と3に互換性がある.xは完全に可能である.Pythonの__を使うことでfuture__imports.Python 3で書かれたコードをPython 2で実行することができます.
詳細はこちらをご覧ください
# # 。
"""
"""
"""
####################################################
## 1.
####################################################
#
3 # => 3
#
1 + 1 # => 2
8 - 1 # => 7
10 * 2 # => 20
35 / 5 # => 7
# 。 。
5 / 2 # => 2
#
2.0 #
11.0 / 4.0 # => 2.75
# 。
5 // 3 # => 1
5.0 // 3.0 # => 1.0
-5 // 3 # => -2
-5.0 // 3.0 # => -2.0
# （ ）
# '/'。
from __future__ import division
11/4 # => 2.75
11//4 # => 2
#
7 % 3 # => 1
#
2**4 # => 16
#
(1 + 3) * 2 # => 8
#
# 「and」 「or」
True and False #=> False
False or True #=> True
#
0 and 2 #=> 0
-5 or 0 #=> -5
0 == False #=> True
2 == True #=> False
1 == True #=> True
# 「not」
not True # => False
not False # => True
# 「==」
1 == 1 # => True
2 == 1 # => False
#「!=」
1 != 1 # => False
2 != 1 # => True
#
1 < 10 # => True
1 > 10 # => False
2 <= 2 # => True
2 >= 2 # => True
# ！
1 < 2 < 3 # => True
2 < 3 < 2 # => False
# 「"」 「'」
"This is a string."
'This is also a string.'
# ！
"Hello " + "world!" # => "Hello world!"
# 「+」
"Hello " "world!" # => "Hello world!"
#
"Hello" * 3 # => "HelloHelloHello"
#
"This is a string"[0] # => 'T'
# 「%」
# 「%」 Python 3.1
# ， 。
x = 'apple'
y = 'lemon'
z = "The items in the basket are %s and %s" % (x,y)
#
#
"{} is a {}".format("This", "placeholder")
"{0} can be {1}".format("strings", "formatted")
# ，
"{name} wants to eat {food}".format(name="Bob", food="lasagna")
# None
None # => None
# 「==」 None
# 「is」
"etc" is None # => False
None is None # => True
# 「is」 。
# ，
# 。
# 。
# ：
# - None
# - (e.g., 0, 0L, 0.0, 0j)
# - (e.g., '', (), [])
# - (e.g., {}, set())
# -
# ：https://docs.python.org/2/reference/datamodel.html#object.__nonzero__
# （ bool() True）
bool(0) # => False
bool("") # => False
####################################################
## 2.
####################################################
# Python print
print "I'm Python. Nice to meet you!" # => I'm Python. Nice to meet you!
#
input_string_var = raw_input("Enter some data: ") # String
input_var = input("Enter some data: ") # Int
# ： input()
# ： Python 3，input() ， raw_input() input()
#
some_var = 5 #
some_var # => 5
# 。
# 「 」 。
some_other_var #
# 「if」 C 「?:」
"yahoo!" if 3 > 2 else 2 # => "yahoo!"
# Lists
li = []
# list
other_li = [4, 5, 6]
# append list
li.append(1) # li is now [1]
li.append(2) # li is now [1, 2]
li.append(4) # li is now [1, 2, 4]
li.append(3) # li is now [1, 2, 4, 3]
# pop list
li.pop() # => 3 and li is now [1, 2, 4]
#
li.append(3) # li is now [1, 2, 4, 3] again.
# list
li[0] # => 1
# 「=」
li[0] = 42
li[0] # => 42
li[0] = 1 # Note: setting it back to the original value
# Look at the last element
#
li[-1] # => 3
# IndexError
li[4] # Raises an IndexError
# list
li[1:3] # => [2, 4]
#
li[2:] # => [4, 3]
#
li[:3] # => [1, 2, 4]
#
li[::2] # =>[1, 4]
# list
li[::-1] # => [3, 4, 2, 1]
# li[ ： ： ]
# 「del」
del li[2] # li is now [1, 2, 3]
# list
li + other_li # => [1, 2, 3, 4, 5, 6]
# ：li other_list
# 「extend()」 list
li.extend(other_li) # Now li is [1, 2, 3, 4, 5, 6]
#
li.remove(2) # li is now [1, 3, 4, 5, 6]
li.remove(2) # ValueError， 2 li
#
li.insert(1, 2) # li is now [1, 2, 3, 4, 5, 6] again
#
li.index(2) # => 1
li.index(7) # ValueError， 7 li
# 「in」 list
1 in li # => True
# 「len()」 list
len(li) # => 6
# 「Tuples」 list，
tup = (1, 2, 3)
tup[0] # => 1
tup[0] = 3 # Raises a TypeError
# Tuples list
len(tup) # => 3
tup + (4, 5, 6) # => (1, 2, 3, 4, 5, 6)
tup[:2] # => (1, 2)
2 in tup # => True
# tuples（ lists）
a, b, c = (1, 2, 3) # a is now 1, b is now 2 and c is now 3
d, e, f = 4, 5, 6 # you can leave out the parentheses
# Tuples
g = 4, 5, 6 # => (4, 5, 6)
#
e, d = d, e # d is now 5 and e is now 4
# map
empty_dict = {}
#
filled_dict = {"one": 1, "two": 2, "three": 3}
# 「[]」
filled_dict["one"] # => 1
# 「keys()」 list
filled_dict.keys() # => ["three", "two", "one"]
# ：
#
# Get all values as a list with "values()"
# 「values()」 list
filled_dict.values() # => [3, 2, 1]
# ：
# 「in」
"one" in filled_dict # => True
1 in filled_dict # => False
# KeyError
filled_dict["four"] # KeyError
# 「get()」 KeyError
filled_dict.get("one") # => 1
filled_dict.get("four") # => None
# get ，
filled_dict.get("one", 4) # => 1
filled_dict.get("four", 4) # => 4
# filled_dict.get("four") None
# （get ）
# list
filled_dict["four"] = 4 # now, filled_dict["four"] => 4
# 「setdefault()」
filled_dict.setdefault("five", 5) # filled_dict["five"] is set to 5
filled_dict.setdefault("five", 6) # filled_dict["five"] is still 5
empty_set = set()
# set
some_set = set([1, 2, 2, 3, 4]) # some_set is now set([1, 2, 3, 4])
# ，
another_set = set([4, 3, 2, 2, 1]) # another_set is now set([1, 2, 3, 4])
# Python 2.7 ，{} set
filled_set = {1, 2, 2, 3, 4} # => {1, 2, 3, 4}
# set
filled_set.add(5) # filled_set is now {1, 2, 3, 4, 5}
# set 「&」
other_set = {3, 4, 5, 6}
filled_set & other_set # => {3, 4, 5}
# set 「|」
filled_set | other_set # => {1, 2, 3, 4, 5, 6}
# set 「-」
{1, 2, 3, 4} - {2, 3, 5} # => {1, 4}
# set 「^」
{1, 2, 3, 4} ^ {2, 3, 5} # => {1, 4, 5}
#
{1, 2} >= {1, 2, 3} # => False
#
{1, 2} <= {1, 2, 3} # => True
# 「in」
2 in filled_set # => True
10 in filled_set # => False
####################################################
## 3.
####################################################
#
some_var = 5
# if 。 Python ！
if some_var > 10:
print "some_var is totally bigger than 10."
elif some_var < 10: # elif
print "some_var is smaller than 10."
else: #
print "some_var is indeed 10."
"""
prints:
dog is a mammal
cat is a mammal
mouse is a mammal
"""
for animal in ["dog", "cat", "mouse"]:
# {0} （ ）
print "{0} is a mammal".format(animal)
"""
「range(number)」
prints:
0
1
2
3
"""
for i in range(4):
print i
"""
「range(number)」
prints:
4
5
6
7
"""
for i in range(4, 8):
print i
"""
While
prints:
0
1
2
3
"""
x = 0
while x < 4:
print x
x += 1 # Shorthand for x = x + 1
# try/except
# Python2.6 ：
try:
# 「raise」
raise IndexError("This is an index error")
except IndexError as e:
pass # Pass 。
except (TypeError, NameError):
pass # ，
else: # try/except 。 except
print "All good!" # try
finally: #
print "We can clean up resources here"
# with ， try/finally
with open("myfile.txt") as f:
for line in f:
print line
####################################################
## 4.
####################################################
# 「def」
def add(x, y):
print "x is {0} and y is {1}".format(x, y)
return x + y # return
#
add(5, 6) # => prints out "x is 5 and y is 6" and returns 11
# ，
add(y=6, x=5) # Keyword arguments can arrive in any order.
# ， 「*」
def varargs(*args):
return args
varargs(1, 2, 3) # => (1, 2, 3)
# ， 「**」
def keyword_args(**kwargs):
return kwargs
#
keyword_args(big="foot", loch="ness") # => {"big": "foot", "loch": "ness"}
# ，
def all_the_args(*args, **kwargs):
print args
print kwargs
"""
all_the_args(1, 2, a=3, b=4) prints:
(1, 2)
{"a": 3, "b": 4}
"""
# ， ， 「*」 「**」
args = (1, 2, 3, 4)
kwargs = {"a": 3, "b": 4}
all_the_args(*args) # equivalent to foo(1, 2, 3, 4)
all_the_args(**kwargs) # equivalent to foo(a=3, b=4)
all_the_args(*args, **kwargs) # equivalent to foo(1, 2, 3, 4, a=3, b=4)
def pass_all_the_args(*args, **kwargs):
all_the_args(*args, **kwargs)
print varargs(*args)
print keyword_args(**kwargs)
#
x = 5
def set_x(num):
# x x
x = num # => 43
print x # => 43
def set_global_x(num):
global x
print x # => 5
x = num # x 6
print x # => 6
set_x(43)
set_global_x(6)
# Python
def create_adder(x):
def adder(y):
return x + y
return adder
add_10 = create_adder(10)
add_10(3) # => 13
#
(lambda x: x > 2)(3) # => True
(lambda x, y: x ** 2 + y ** 2)(2, 1) # => 5
#
map(add_10, [1, 2, 3]) # => [11, 12, 13]
map(max, [1, 2, 3], [4, 2, 1]) # => [4, 2, 3]
filter(lambda x: x > 5, [3, 4, 5, 6, 7]) # => [6, 7]
# list map
[add_10(i) for i in [1, 2, 3]] # => [11, 12, 13]
[x for x in [3, 4, 5, 6, 7] if x > 5] # => [6, 7]
####################################################
## 5.
####################################################
# object
class Human(object):
# 。
species = "H. sapiens"
# ， 。
# Python ，
# 。 。
def __init__(self, name):
#
self.name = name
#
self.age = 0
# 。 「self」
def say(self, msg):
return "{0}: {1}".format(self.name, msg)
#
#
@classmethod
def get_species(cls):
return cls.species
#
@staticmethod
def grunt():
return "*grunt*"
# 「property」 getter
# age()
@property
def age(self):
return self._age
# set
@age.setter
def age(self, age):
self._age = age
#
@age.deleter
def age(self):
del self._age
#
i = Human(name="Ian")
print i.say("hi") # prints out "Ian: hi"
j = Human("Joel")
print j.say("hello") # prints out "Joel: hello"
#
i.get_species() # => "H. sapiens"
#
Human.species = "H. neanderthalensis"
i.get_species() # => "H. neanderthalensis"
j.get_species() # => "H. neanderthalensis"
#
Human.grunt() # => "*grunt*"
#
i.age = 42
#
i.age # => 42
#
del i.age
i.age # => raises an AttributeError
####################################################
## 6.
####################################################
#
import math
print math.sqrt(16) # => 4
#
from math import ceil, floor
print ceil(3.7) # => 4.0
print floor(3.7) # => 3.0
#
# ：
from math import *
#
import math as m
math.sqrt(16) == m.sqrt(16) # => True
# you can also test that the functions are equivalent
from math import sqrt
math.sqrt == m.sqrt == sqrt # => True
# Python python 。 。
# 。
# 「dir」
import math
dir(math)
# Python 「math.py」 ，
# Python 。
# Python 。
####################################################
## 7.
####################################################
# Generators help you make lazy code
def double_numbers(iterable):
for i in iterable:
yield i + i
# A generator creates values on the fly.
# Instead of generating and returning all values at once it creates one in each
# iteration. This means values bigger than 15 wont be processed in
# double_numbers.
# Note xrange is a generator that does the same thing range does.
# Creating a list 1-900000000 would take lot of time and space to be made.
# xrange creates an xrange generator object instead of creating the entire list
# like range does.
# We use a trailing underscore in variable names when we want to use a name that
# would normally collide with a python keyword
xrange_ = xrange(1, 900000000)
# will double all numbers until a result >=30 found
for i in double_numbers(xrange_):
print i
if i >= 30:
break
# Decorators
# in this example beg wraps say
# Beg will call say. If say_please is True then it will change the returned
# message
from functools import wraps
def beg(target_function):
@wraps(target_function)
def wrapper(*args, **kwargs):
msg, say_please = target_function(*args, **kwargs)
if say_please:
return "{} {}".format(msg, "Please! I am poor :(")
return msg
return wrapper
@beg
def say(say_please=False):
msg = "Can you buy me a beer?"
return msg, say_please
print say() # Can you buy me a beer?
print say(say_please=True) # Can you buy me a beer? Please! I am poor :(