Category: Python

speed of light

speed_of_light = 299792458
billionth = 1.0 /1000000000
nanostick = speed_of_light * billion
print nanostick

variable changes with faster processer, even in the same expression, divede by cycles_per_second.

speed_of_light = 299792458
cycles_per_second = 2700000000. # 2.7GHz

cycle_distance = speed_of_light / cycles_per_second

cycles_per_second = 2800000000. # 2.8GHz
print(cycle_distance)

cycle_distance = speed_of_light / cycles_per_second
print(cycle_distance)

Finding Strings in strings

pythagoras = 'There is geometry in the humming of the string, there is music in the spacing of the spheres'
print(pythagoras.find('string'))
print(pythagoras[40:])
print(pythagoras.find('algebra'))

danton = "De l'audance, encore de l'audace, toujours de l'audace"
print(danton.find('audace'))
print(danton.find('audace', 0))
print(danton.find('audace', 5))
print(danton.find('audace', 6))
print(danton[6:])

link procedure

def get_next_target(page):
  start_link = page.find('<a href=')
  start_quote = page.find('"', start_link)
  end_quote = page.find('"', start_quote + 1)
  url = page&#91;start_quote + 1:end_quote&#93;
  return url, end_quote
  
print(get_next_target('this is a <a href="www.yahoo.co.jp">link</a>'))

How to crawler get a link from webpages.

def print_all_links(page):
  while True:
    url, endpos = get_next_target(page)
    if url:
      print(url)
      page = page[endpos:]
    else:
      break
  
print_all_links(get_page('http://yahoo.co.jp'))

find last position

def find_last(s, t):
  last_pos = -1
  while True:
    pos = s.find(t, last_pos)
    if pos == -1:
      return last_pos
      last_pos = pos

Python基礎

python3とpython2では記法が異なっている点があるので注意が必要です。

print ("hello world!")

変数

msg = "hello world"
print (msg)

整数と小数の演算は小数、整数同士の割り算は、小数点以下切り捨てとなります。

繰り返し処理

print (u"無駄"*10)

\\, \*なども

改行表現

print ("""<html>
<body>
</body>
</html>""")

整数値と文字列はpythonでは明示する

print (5 + int("5"))
print ("i am " + str(20) + "years old.")

配列、存在チェック

sales = [200, 100, 342, 1230, 122]
print (100 in sales)

ソート、reverse

sales = [52, 100, 80, 45]
sales.sort()
print (sales)

タプル：変更不可

a = (2, 5, 8)
print (a * 3)

セット:重複を許さない

a = set([1, 2, 3, 4])
print (a)

差集合

a = set([1, 2, 3, 4])
b = set([4, 5, 6, 7])
print (b - a)

辞書

sales = {"yamada": 200, "yoshida": 300, "sakura": 240}
print (sales)

key、value、items(一覧)

sales = {"yamada": 200, "yoshida": 300, "sakura": 240}
print (sales.values())

文字列へのデータ組み込み

a = 10
b = 123.345
c = "sakaki"
d = {"yamada":200, "yoshimoto": 300}
print ("age: %d" % a)

条件分岐

score = 70
if score > 60:
    print ("ok")

条件分岐2

score = 55
if score > 60:
    print ("ok")
elif score > 50:
    print ("soso")
else:
    print ("NG!")

forループ

sales = [13, 235, 312, 2232]
for sale in sales:
    print (sale)

繰り返し処理　※インデントに注意

for i in range(10):
    print(i)

空処理

def hello2():
    pass

python module:
https://docs.python.org/3/library/index.html