python學習記錄-基礎 2014/02/28

整數

整數沒有上下限

>>> 27**100
136891479058588375991326027382088315966463695625337436471480190078368997177499076593800206155688941388250484440597994042813512732765695774566001

運算符

「//」 整除，會舍掉小數

>>> 5/3
1.6666666666666667
>>> 5//3
1
>>> 1/3
0.3333333333333333
>>> 1//3
0

浮點數

數值大小有上下限

>>> 500 ** 10000
50123727492064520092975559337429777493215677813384258394214290422792395309507840401891106962484224133615218492862058372081327443176891273016482168954795781185874209111160612289384877840210668133773552608102495789572162971239408991402272898479042193487906171309477254859220910820260373325729016674503082447394244693204052866594230899522151692248580978679514873159608242138078045415083878886701652303992237313103864199817534633842287720605482756450323537116934243653732537194326201888943493999035280474169717550522925449533180568976487439798992327523884152357361057668549072680285981924365374573246969209535613981945223363845705677002140024059488571852502696627853310147222972014403229078617683030314562366575549636043559949032365057251302556823481370490308311044496739031547850764310970927247021881187568482842876484689226538219502388665212371709231922579559450496040904493536815952132377847701774177761214218182100677141066255918497666099992572505904049332246474851616769753973094044884008245586479442761583605455479138568037624055570570531064041891481843272563257390054437582428922511005538103757211948878280213725454074308035962175438145690867240884031289727385298380658314122216070772882205303823879152593490031895854603124993202409812087282808852271258570276219582296999973714901027841127326795584530703442296230169334181999714199012961264843398162089479207901926977921859076100544091077762713076480909813109663248283876923124135477731056050643391668045044017100307507263811214698074886297294628992974267525820335892544444475612848585688414487741496924252866696357856863799077635679894424436807127550991308783249322835872771946357693791416553243160873629582393585085960295650110954423020715034293137454460173052854299028735511722685743587899263467753878307673194310143123104521978173337460860245616897102691669313615897977634335639754832732268983482680825173463654102107791004977902364226845796605479780482473635564413756483059519545171023756787906643963725886300443117601838677612512864890762997577068276373419161219788564898787441416567704296671154985658865359840878550051068542231710029863654309594178120066568691080667604179199166051480563200103566187484165258832072570720461839214204148422561219245719397454209905373084759786333770919908794824052037401204349485646630570708124748197220294636781919520959588557656498547979037241519067766700059873115184981482178012359220891764214203015203007234548143338202832965319284331289712974623643198103775067314569890817138584269492244527481002591223841622152296435131063071619884393288982107203076750872709118940584271360022469611057323590654487884690538707785771404681713726381894993199978081843221672814332675100208457599198444896312642932985562647269302463262028438918956967062661514148648080466745376642005249620889789950533979690707574953792504763948109976339412295427166835421439046176707541894989075725981519173526480997048007062336126157338651442354211686995917622700105156341579006661673082538988255026054950735611492658066191035822218637505233662626639640292063245559840789667724907576132819763286725084937878205431297874214624437295115358032473687577301593058918200555261366338070820887209014075112110807018641953433188242338236723194411672498587238452794622953397520040600900117580255321421115358375633515710076594190601645062272105605478560790718561440870957060982872953219432407348830330216903638196086438857619132622206324453373315658137540865900128532168480533536861756828334686721632905273266262006365874183166878796970321334047354274354242850814109125541945176998846685608920845052074190770209960048333549852120116390668193006699333623609415279364052909468601499104708856710503626024115298446714887071349017171054461167876402810686582547200604196386595264027635945020431098873821970582034081247681546909746122619378846567012113745526738041727543255757287160881312674110642706771507770044620296331902892728196903166166273540695217507064344662587800429421752592573278754447148751764228781666557521242589820580414821153601185094066560314402509846190078790285114197864868483598968295492158738735949917449262470887954949502569936562118054895068509783958568815749784980380282171425137258005269641272443470367402200106381611425188607923274339699159683742358436639818922646488141983311990075392845387921372335899188516442716809635327286105054547268880545110364384801376484356050205731956421746314565970754902508422620252826092706407198666739254872645967117287664685733084358906403164210059943184541795071181205903344356711221275796623109134708655591318283401499662873785986070636317954455864445598819923903268322058566473224241491330029180516888395841621464303650247861778359615749323279426064558223801086770534255914026422880866561010321483099701044644515351017272800695566940530686856928442334505216207613310108275848420459286481277699764668627984850691186695648583589313960845087172710034795436370637316353900825053008679035618390828048093356139876547239100635092411587479579690876916276493516268512121725058717098189617733366182452151774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>>> 500.0 ** 10000
Traceback (most recent call last):
  File "<pyshell#1>", line 1, in <module>
    500.0 ** 10000
OverflowError: (34, 'Result too large')

浮點數支持科學記數法和複數

>>> 8.8 ** -5.4
7.939507629591553e-06
>>> 2.3e02
230.0
>>> 

>>> 1j
1j
>>> 1j * 1j
(-1+0j)
>>>

模塊的導入

>>> import math
>>> math.pi
3.141592653589793
>>> from math import *
>>> pi
3.141592653589793
>>> from math import pi
>>> pi
3.141592653589793
>>>

字符串

'123'

"123"

"""123"""    # 能夠寫多行

>>> a  = """
ss;fdsfsdf
sfsdfsfsdf
"""
>>> a
'\nss;fdsfsdf\nsfsdfsfsdf\n'

字符串拼接

>>> 'abc' * 3
'abcabcabc'

列出模塊的全部函數

>>> dir(math)
['__doc__', '__loader__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'log2', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc']

python內置函數

>>> dir(__builtins__)
['ArithmeticError', 'AssertionError', 'AttributeError', 'BaseException', 'BlockingIOError', 'BrokenPipeError', 'BufferError', 'BytesWarning', 'ChildProcessError', 'ConnectionAbortedError', 'ConnectionError', 'ConnectionRefusedError', 'ConnectionResetError', 'DeprecationWarning', 'EOFError', 'Ellipsis', 'EnvironmentError', 'Exception', 'False', 'FileExistsError', 'FileNotFoundError', 'FloatingPointError', 'FutureWarning', 'GeneratorExit', 'IOError', 'ImportError', 'ImportWarning', 'IndentationError', 'IndexError', 'InterruptedError', 'IsADirectoryError', 'KeyError', 'KeyboardInterrupt', 'LookupError', 'MemoryError', 'NameError', 'None', 'NotADirectoryError', 'NotImplemented', 'NotImplementedError', 'OSError', 'OverflowError', 'PendingDeprecationWarning', 'PermissionError', 'ProcessLookupError', 'ReferenceError', 'ResourceWarning', 'RuntimeError', 'RuntimeWarning', 'StopIteration', 'SyntaxError', 'SyntaxWarning', 'SystemError', 'SystemExit', 'TabError', 'TimeoutError', 'True', 'TypeError', 'UnboundLocalError', 'UnicodeDecodeError', 'UnicodeEncodeError', 'UnicodeError', 'UnicodeTranslateError', 'UnicodeWarning', 'UserWarning', 'ValueError', 'Warning', 'WindowsError', 'ZeroDivisionError', '_', '__build_class__', '__debug__', '__doc__', '__import__', '__loader__', '__name__', '__package__', 'abs', 'all', 'any', 'ascii', 'bin', 'bool', 'bytearray', 'bytes', 'callable', 'chr', 'classmethod', 'compile', 'complex', 'copyright', 'credits', 'delattr', 'dict', 'dir', 'divmod', 'enumerate', 'eval', 'exec', 'exit', 'filter', 'float', 'format', 'frozenset', 'getattr', 'globals', 'hasattr', 'hash', 'help', 'hex', 'id', 'input', 'int', 'isinstance', 'issubclass', 'iter', 'len', 'license', 'list', 'locals', 'map', 'max', 'memoryview', 'min', 'next', 'object', 'oct', 'open', 'ord', 'pow', 'print', 'property', 'quit', 'range', 'repr', 'reversed', 'round', 'set', 'setattr', 'slice', 'sorted', 'staticmethod', 'str', 'sum', 'super', 'tuple', 'type', 'vars', 'zip']

幫助文檔

>>> help(sum)
Help on built-in function sum in module builtins:

sum(...)
    sum(iterable[, start]) -> value
    
    Return the sum of an iterable of numbers (NOT strings) plus the value
    of parameter 'start' (which defaults to 0).  When the iterable is
    empty, return start.

>>> print(sum.__doc__)
sum(iterable[, start]) -> value

Return the sum of an iterable of numbers (NOT strings) plus the value
of parameter 'start' (which defaults to 0).  When the iterable is
empty, return start.

類型轉換

>>> round(8.5)    # 將.5取整到他最接近的偶數
8
>>> round(8.4)
8
>>> round(8.6)
9
>>> float(3)
3.0
>>> int(9.8)
9
>>> str(9.5)
'9.5'
>>> round(-9.5)
-10

trunc直接舍掉小數

>>> math.trunc(8.5)
8
>>> math.trunc(8.4)
8
>>> math.trunc(8.6)
8

>>> math.trunc(-8.1)
-8
>>> math.trunc(-8.5)
-8
>>> math.trunc(-8.9)
-8

floor 向小的取整

>>> math.floor(8.4)
8
>>> math.floor(8.5)
8
>>> math.floor(8.6)
8

>>> math.floor(-8.4)
-9
>>> math.floor(-8.5)
-9
>>> math.floor(-8.6)
-9

ceil向大數取整

>>> math.ceil(8.4)
9
>>> math.ceil(8.5)
9
>>> math.ceil(8.6)
9
>>> math.ceil(-8.4)
-8
>>> math.ceil(-8.5)
-8
>>> math.ceil(-8.6)
-8

變量

變量名區分大小寫

長度無限制，只能以字母、數字、下劃線構成，但不能以數字開頭

不能用關鍵字作變量名

變量必須初始化以後才能使用

賦值

數字及字符串是不可變的，修改數字及字符串，其實就是複製一份而後修改後再賦值。

>>> x, y, z = 1, 'two', 3.0
>>> x
1
>>> y
'two'
>>> z
3.0
>>> x, y, z
(1, 'two', 3.0)

>>> a, b = 5, 9
>>> a, b
(5, 9)
>>> a, b = b, a
>>> a, b
(9, 5)