Recently, I have had many opportunities to analyze data, and I decided to study python a little because I heard that it is good for statistical calculation. It is a memo writing at that time. It's broken here and there.
[Reference] http://docs.python.jp/2/tutorial/index.html
You can use basic operators. Imaginary numbers can also be used naturally.
python
>>> 2
2
>>> 2 + 4 #operator+, -, *, /Such
6
>>> 5/2 #When integers are used, the calculation result is also an integer(Devaluation)
2
>>> 5/2.0 #If you use a floating point number, the calculation result will be a floating point number.
2.5
>>> 1j * 1J #Imaginary number is j or J
(-1+0j)
>>> a=1.5+0.5j #Variable declaration
>>> a.real #Get the real part
1.5
>>> a.imag #Acquisition of imaginary part
0.5
Indicates a character string in single or double quotes. Escape special characters with a backslash.
python
>>> 'spam eggs' #Single quote
'spam eggs'
>>> "doesn't" #Double quote
"doesn't"
>>> '"Yes," he said.' #Double quotes within single quotes are displayed
'"Yes," he said.'
>>> "\"Yes,\" he said." #Double quotes inside double quotes are escaped with a backslash
'"Yes," he said.'
>>> '"Isn't," she said.' #Single quotes inside single quotes are in error
File "<stdin>", line 1
'"Isn't," she said.'
^
SyntaxError: invalid syntax
>>> '"Isn\'t," she said.' #Even if you insert a backslash, it is displayed together with the backslash
'"Isn\'t," she said.'
Intuitive operation of character strings
python
>>> word = 'Help' + 'A' #Addition of strings
>>> word
'HelpA'
>>> string = 'str' 'ing' #+ Can be omitted
>>> string
'string'
>>> 'str'.strip() 'ing' #But don't omit it in this case
File "<stdin>", line 1
'str'.strip() 'ing'
^
SyntaxError: invalid syntax
It is also possible to operate character strings with subscripts. If omitted, it will be complemented appropriately.
>>> word
'HelpA'
>>> word[4] # index 4,Get the 5th character
'A'
>>> word[0:2] # index 0,Get 1
'He'
>>> word[:2] #index first~Get up to 1
'He'
>>> word[2:] # index 2~Get to the end
'lpA'
>>> word[-1] #Minus notation is also possible.Index from the end
'A'
Cannot be assigned to a string
python
>>> word[0] = 'x' #Error when trying to assign
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment
Lists are separated by commas and enclosed in parentheses. The types of list elements do not have to be the same. You can also nest lists.
python
>>> a = ['spam', 'eggs', 100, 1234] #List declaration
>>> a
['spam', 'eggs', 100, 1234]
>>> a[3] #Can also be specified by index
1234
>>> a[0:2] = [] #Delete element
>>> a
[100, 1234]
>>> a[1:1] = ['bletch', 'xyzzy'] #Add element
>>> a
[100, 'bletch', 'xyzzy', 1234]
Can be assigned collectively.
python
>>> a, b = 0, 1 # a =0 and b=Run 1
>>> a
0
>>> b
1
if
You can add as many elifs as you like. You can also add else. if ... elif ... elif ... is a substitute for switch statements and case statements.
python
>>> x = int(raw_input("Please enter an integer: ")) #Input from command line
Please enter an integer: 42
>>> if x < 0: #The beginning of the if statement
... x = 0
... print 'Negative changed to zero'
... elif x == 0: #Add condition with elif
... print 'Zero'
... elif x == 1:
... print 'Single'
... else: #If the condition is not met, set to else
... print 'More'
...
More
for
The for statement iterates over lists and strings
python
>>> a = ['cat', 'window', 'defenestrate']
>>> for x in a: #Iterative processing for each element of a
... print x, len(x) # len()Get the length with
...
cat 3
window 6
defenestrate 12
You can use the range () function when iterating over a sequence.
python
>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(5,10) #Use by specifying the range
[5, 6, 7, 8, 9]
>>> range(1, 10, 2) #Use by specifying the range and how to increase
[1, 3, 5, 7, 9]
>>> a = ['Mary', 'had', 'a', 'little', 'lamb']
>>> for i in range(len(a)): #Operate using range and len
... print i, a[i]
...
0 Mary
1 had
2 a
3 little
4 lamb
break
The break statement is used to end the operation in the middle. Exit the innermost for and while.
python
>>> #Check if it is a prime number
>>> for n in range(2, 10):
... for x in range(2,n):
... if n % x == 0:
... print n, 'equals', x, '*', n/x
... break
... else:
... print n, 'is a prime number'
...
2 is a prime number
3 is a prime number
4 equals 2 * 2
5 is a prime number
6 equals 2 * 3
7 is a prime number
8 equals 2 * 4
9 equals 3 * 3
pass
The pass statement does nothing. Used when you have to write a sentence but there is no processing.
python
>>> #Smallest class
>>> class MyEmptyClass:
... pass
...
def indicates the function declaration. You can change the name by assigning a function to a variable.
python
>>> #Output Fibonacci sequence up to n
>>> def fib(n):
... a, b = 0, 1
... while a < n:
... print a, #Hitting a comma does not break the output
... a, b = b, a+b
...
>>> fib(100)
0 1 1 2 3 5 8 13 21 34 55 89
>>> f = fib #Give the function a different name
>>> f(200)
0 1 1 2 3 5 8 13 21 34 55 89 144
Return to return a value. Default arguments and keyword arguments can be used.
python
>>> def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
... print "-- This parrot wouldn't", action,
... print " if you put", voltage, "volts through it."
... print "-- Lovely plumage, the", type
... print "-- It's", state, "!"
...
>>> parrot(100) #Use default values except voltage
-- This parrot wouldn't voom if you put 100 volts through it.
-- Lovely plumage, the Norwegian Blue
-- It's a stiff !
>>> parrot(action = 'VOOOOM', voltage = 100000) #Pass by specifying a keyword
-- This parrot wouldn't VOOOOM if you put 100000 volts through it.
-- Lovely plumage, the Norwegian Blue
-- It's a stiff !
It can also accept variadic arguments. Use \ * name to receive a tuple with positional arguments beyond the list of formal arguments, and ** name to receive a dictionary containing all keyword arguments except those corresponding to the previous formal arguments. ..
python
>>> def cheeseshop(kind, *arguments, **keywords):
... print "-- Do you have any", kind, "?"
... print "-- I'm sorry, we're all out of", kind
... for arg in arguments:
... print arg
... print "-" * 40
... keys = sorted(keywords.keys())
... for kw in keys:
... print kw, ":", keywords[kw]
...
>>> cheeseshop("Limburger",
... "It's very runny, sir.", # arguments
... "It's really very, VERY runny, sir.", # arguments
... shopkeeper="Michael Palin", # keywords
... client="John Cleese", # keywords
... sketch="Cheese Shop Sketch") # keywords
-- Do you have any Limburger ?
-- I'm sorry, we're all out of Limburger
It's very runny, sir.
It's really very, VERY runny, sir.
----------------------------------------
client : John Cleese
shopkeeper : Michael Palin
sketch : Cheese Shop Sketch
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