Python基本用法, 快速查詢用, 另外DataCamp有提供相當多資料科學學習資源, 也有Python cheat sheet可供下載, 在此附上連結 |
DataCamp提供相當多資料科學學習資源, 資料科學所使用的工作過多導致學習上會讓新手陷入困難 , 看小抄就是一個很好的方法用來快速複習語法, 裡面提供Python.Keras.pandas.PySpark.......等小抄, 有興趣可以下載來看看
下面整理一些基本的語法供快速查詢用：
if簡約寫法
(0 if x==“?“ else float(x))
dict寫法
d = { ‘a’:1, ‘b’:2, ‘c’:3 }
d = dict(a=1,b=2,c=3)
d= dict(zip([a,b,c],[1,2,3]))
d = dict([(‘a’,1),(‘b’,2),(‘c’,3)])
for key in d:
print key
for key in d.keys():
print key
for value in d.values:
print value
for key,value in d.items():
print (key,value)
# 找key值是否存在 or try catch
if dict.has_key('key'):
print 'find key'
if key in dict:
print 'find key'
name = some_dict.get('name', 'Bob')#找不到回傳Bob
# dict append data
dict.update({'key':'value','key1':'value1'})
dict['new'] = 'values2'
del dict['new']
kList = list(d.keys()) vList=list(d.values())
list(zip(d.items())) >>> [(‘a’,1),(‘b’,2),(‘c’,3)] list(zip(d.values(),d.keys)) >>>[(1:’a’),(2:’b’),(3,’c’)] ## get dict row tuple field, value = d.items()[0]
d = {‘amy’:(20,50,70), ‘boy’:(50,40,70)}
for x in sorted(d.values())
print (x, d[x])
def foo(item):
return item[1][2] #依照tuple第二欄排序
for item sorted(d, key=foo):
print(item)
#移除重複值
list_fix = {each[‘EmployeeId’] : each for each in list}.values()
li = [0,1,2,3,4,5,6]
for i , x in enumerate(li):
if x % 2 == 0:
del li[i]
#defaultdict有預設值的字典 #OrderedDict 具有順序的字典 #frozenset 不可變的集合
(lambda x,y : x if x > y else y)( 3 , 4 ) #宣告lambda後直接呼叫 li = [(‘a’,1),(‘b’,2)] sorted( li , key=lambda item: item[0] ) sorted( li , key=lambda item: len(item[0]) )
filter
>>> def fn(x): ... return x if x > 5 else None ... >>> a = [1, 2, 3, 4, 5, 6, 7, 8, 9] >>> b = filter(fn, a) >>> b [6, 7, 8, 9]
map
>>> a = [1, 2, 3, 4, 5, 6, 7, 8, 9] >>> def fn(x): ... return x*2 >>> c = map(fn, a) >>> c [2, 4, 6, 8, 10, 12, 14, 16, 18]
reduce
>>> a = [1, 2, 3, 4, 5, 6, 7, 8, 9] >>> def fn(x, y): ... return x+y >>> d = reduce(fn, a) >>> d 45
decorator
def use_logging(func):
def wrapper():
logging.warn("%s is running" % func.__name__)
return func()
return wrapper
@use_logging
def foo():
print("i am foo")
foo()
def use_logging(level):
def decorator(func):
def wrapper(*args, **kwargs):
if level == "warn":
logging.warn("%s is running" % func.__name__)
elif level == "info":
logging.info("%s is running" % func.__name__)
return func(*args)
return wrapper
return decorator
@use_logging(level="warn")
def foo(name='foo'):
print("i am %s" % name)
foo()
try catch
import sys
try:
f = open('myfile.txt')
s = f.readline()
i = int(s.strip())
except OSError as err:
print("OS error: {0}".format(err))
except ValueError:
print("Could not convert data to an integer.")
except:
print("Unexpected error:", sys.exc_info()[0])
else:
i = i + 10
print("Open file successs.")
我們也可以先建立一個 exception 的 calss ，然後拋出我們定義的異常
class MyError(Exception):
def __init__(self, value):
self.value = value
def __str__(self):
return repr(self.value)
@property : 類似C#的getter setter
class Egg(object):
def __init__(self, price):
self._price = price
@property
def price(self):
return self._price * RATE
@price.setter
def price(self, value):
self._price = value
Class (父類別不可宣告的寫法)
import random
from abc import ABCMeta, abstractmethod
class GuessGame(metaclass=ABCMeta):
@abstractmethod
def message(self, msg):
pass
@abstractmethod
def guess(self):
pass
def go(self):
self.message(self.welcome)
number = int(random.random() * 10)
while True:
guess = self.guess();
if guess > number:
self.message(self.bigger)
elif guess < number:
self.message(self.smaller)
else:
break
self.message(self.correct)
Class 全域變數的寫法
class TestClass():
g_c = 0
def __init__(self):
self.g_c2 = 4
def run(self):
TestClass.g_c = 1
self.g_c2 = 5
t = TestClass()
t.run()
t2 = TestClass()
t.g_c, t.g_c2, t2.g_c, t2.g_c2
# >>> (1, 5, 1, 4)
繼承
class ConsoleGame(GuessGame):
def __init__(self):
self.welcome = "歡迎"
self.prompt = "輸入數字："
self.correct = "猜中了"
self.bigger = "你猜的比較大"
self.smaller = "你猜的比較小"
def message(self, msg):
print(msg)
def guess(self):
return int(input(self.prompt))
game = ConsoleGame()
game.go()
如果你真的想要模擬Java中interface的作用，則可以定義一個抽象類別，完全沒有實作的方法即可
import random
from abc import ABCMeta, abstractmethod
class Flyer(metaclass=ABCMeta): # 就像是Java中的interface
@abstractmethod
def fly(self):
pass
class Bird:
pass
class Sparrow(Bird, Flyer): # 就像Java中繼承Bird類別並實作Flyer介面
def fly(self):
print('麻雀飛')
s = Sparrow()
s.fly()
http request
import request
root_url = "http://xxx.xxx.xxx"
def query_data(field='all' , name=None, params=None):
header={'id':'test'}
if not params:
params={}
if field == 'all':
return requests.get(root_url + 'all')
url = '%s/%s/%s'%(root_url,field,name)
print url
response =requests.get(url, params=params, headers=headers)
if not response.status_code == requests.codes.ok:
raise Exception('fail') + str(response.status_code)
return response
response = query_data('aaa', 'bbb')
response.json()
Request try except
import request
try:
r=request.get(url, timeout=3)
r.raise_for_status()#回應狀態是400~599,print此函數可以取得更多資訊
except requests.exceptions.RequestException as ex1:
print '404-HTTP請求有錯誤'
except requests.exceptions.HTTPError as ex2:
print '回應不合法的HTTP內容'
except requests.exceptions.ConnectionError as ex3:
print '網路orDNS有錯誤'
except requests.exceptions.Timeout as ex4:
print '408-當HTTP請求超過期限'
except requests.exceptions.TooManyRedirects as ex5:
print '轉址超過設定的最大值'
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