When I try to use it after a long time, I forget various things, so I wrote a memo like Bootcamp. Below is an example of how to use it on Ubuntu. In addition, it is Python 2 system, so I do not know.
First, prepare tools for installing various Python libraries.
easy_install
$ sudo apt-get install python-setuptools
pip
$ sudo apt-get install python-pip
If you need the library, add it with the pip command. (Example: feedparser)
(Example)
$ sudo pip install feedparser
When via a proxy.
(Example)
$ sudo pip install feedparser --proxy proxy.yourdomain.xx:8080
Executing the file that describes the script (eg my_python.py).
$ python my_python.py
You can create common rules for projects, but the shortcut is to comply with PEP8.
There is also a Google Python Style Guide.
If you want to quickly remember how to use it, the contents of this page will do the trick, but if you want to start programming in earnest, it is better to read the above rules. (As with the notation, various techniques can be helpful)
Below are just the main points.
With 4 spaces. (Do not use tabs)
Do not put spaces inside parentheses, square brackets, or curly braces.
# Yes:
spam(ham[1], {eggs: 2}, [])
# No:
spam( ham[ 1 ], { eggs: 2 }, [ ] )
Do not put spaces before commas, semicolons, and colons. Insert a space after the comma, semicolon, or colon other than the end of the line.
# Yes:
if x == 4:
print x, y
x, y = y, x
# No:
if x == 4 :
print x , y
x , y = y , x
Do not put spaces before opening the arguments, the array, the parentheses that start the slice, and the square brackets.
# Yes:
spam(1)
dict['key'] = list[index]
# No:
spam (1)
dict ['key'] = list [index]
Term operators such as assignment (=), comparison (==, <,>,! =, <>, <=,> =, In, not in, is, is not), evaluation (and, or, not) Put spaces on both sides of. Whitespace on both sides of the arithmetic operator is personal judgment, but whitespace characters are inserted on both sides of the term operator.
# Yes:
x == 1
# No:
x<1
Do not put spaces on either side of the ‘=’ symbol for keyword values or initial values.
# Yes:
def complex(real, imag=0.0): return magic(r=real, i=imag)
# No:
def complex(real, imag = 0.0): return magic(r = real, i = imag)
Do not insert spaces to align consecutive lines vertically, as this will reduce maintainability. (:, #, =, etc.):
# Yes:
foo = 1000 # comment
long_name = 2 # comment that should not be aligned
dictionary = {
"foo": 1,
"long_name": 2,
}
# No:
foo = 1000 # comment
long_name = 2 # comment that should not be aligned
dictionary = {
"foo" : 1,
"long_name": 2,
| type | internal | External |
|---|---|---|
| package | lower_with_under | |
| module | lower_with_under | _lower_with_under |
| class | CapWords | _CapWords |
| exception | CapWords | |
| function | lower_with_under() | _lower_with_under() |
| global/Class constant | CAPS_WITH_UNDER | _CAPS_WITH_UNDER |
| global/Class variables | lower_with_under | _lower_with_under |
| Instance variables | lower_with_under | _lower_with_under (protected) or __lower_with_under (private) |
| Method name | lower_with_under() | _lower_with_under() (protected) or __lower_with_under() (private) |
| function/Method parameters | lower_with_under | |
| Local variables | lower_with_under |
Hello World
print 'Hello World'
Super basics of Python.
Block by indent instead of {}.
Styles such as C
if (cond) {
...
}
else {
...
}
Python style
if cond:
...
else:
...
Format output using % d and% s is possible.
ans = 100
print 'answer is %d' % ans
When handling multiple variables, enclose them in ()
count = 1
line = 'hogehoge'
print '%d: %s' % (count, line)
The print statement is automatically broken even if you do not add \ n at the end.
print 'My name is '
print 'John' #Output with line breaks
To prevent line breaks, add , to the end of the character literal. Attach it outside the literal, not inside it.
print 'My name is ', # ,Put on
print 'John' # My name is John.
The comment text is after #
# comment!
var = 10 # initial value
There is no comment-out notation that spans multiple lines.
It can be replaced by using the string notation '''.
(These descriptions are invalidated at compile time)
'''
xxxx
'''
class MyClass:
pass
Unlike Java etc., ; at the end of the line is unnecessary.
Instead, you can't easily break a line in a line.
NG
# NG
msg = 'I am not in Japan now.'
+ 'But I have been there.'
You can start a new line in the middle by adding \ at the end of the line.
OK
# OK
msg = 'I am not in Japan now.' \
+ 'But I have been there.'
Line breaks can be made in the text enclosed by () or [].
Also, the indentation after the line break may be free.
OK
my_method('My', 'Name',
'Is', 'Mike', 'Davis', '.')
def func():
v = [1, 2, 3,
4, 5, 6] #Grammatically OK,Avoid it because it is hard to see.
No need to specify the type in the variable declaration. Numerical values, strings, and arrays are all objects.
val = 10
msg = 'foo'
ary = [1, 2, 3]
c = MyClass()
A form that is often seen in other languages. A line break may be inserted between the elements.
list = [
"Ichiro",
"Jiro",
"Saburo"]
You cannot use | or &.
Use ʻand and ʻor instead.
if a == 1 and b == 2:
# do something
Use True, False.
if True:
print "Always True"
Use None instead of null.
if value is None:
# do something
Note that the notation is different from Java.
data = 100
value = 'even' if data % == 0 else 'odd'
Use def.
In python, functions are also objects.
def func(value):
return value*2
Writing as follows makes the main process easier to understand.
def main():
# do something
...
if __name__ == "__main__":
main()
Use the sys module. ʻArgvs [0]` is the script name.
import sys
argvs = sys.argv
argc = len(argvs)
if (argc != 2):
print 'Usage: %s <file>' % argvs[0]
quit()
print 'param: %s' % argvs[1]
ʻIsis identity (== in Java) ==` is equality (equals () in Java)
Also, unlike Java, all numbers are objects.
That number is a bit confusing to understand.
a = 1
b = 1
if a is b:
print "a is b"
if a == b:
print "a == b"
Intuitively, "a == b" shouldn't be "a is b", When the above is executed, "a is b" is also output.
"a is b"
"a == b"
This seems to be due to the reuse of immutable data and the cache. By the way, probably because the compiler is smart, it will be "a is b" even in the following cases. (Of course a == b)
a = 1 + 3
b = 2 + 2
if a is b:
print "a is b"
In the case of a character string, True is returned with ʻis when it is reused like a numerical value. However, note that ʻis may be False if it is dynamically generated.
x = "X"
a = "XY"
b = x + "Y"
if a == b:
print "a == b"
if a is b:
print "a is b"
output
a == b
By the way, you can get the address of the object by using the ʻid () function. Use it for debugging purposes when ʻis behaves differently than expected.
a = "foo"
print "a at 0x%x" % id(a)
I often forget this, but I use ʻelif`.
if i % 15 == 0:
print 'FizzBuzz'
elif i % 3 == 0:
print 'Fizz'
elif i % 5 == 0:
print 'Buzz'
else:
print i
It is convenient to use range ().
The second argument of range () is the maximum value, but this value is ** not included **.
for i in range(0, 5):
print 'id = %d' % i
output
id = 0
id = 1
id = 2
id = 3
id = 4
When starting from the middle.
for i in range(2, 3):
print 'id = %d' % i
output
id = 2
You can specify step with the third argument. In this case as well, the maximum value of the second argument is not exceeded.
for i in range(0, 10, 2):
print 'id = %d' % i
output
id = 0
id = 2
id = 4
id = 6
id = 8
You can also specify an array.
for i in [0, 2, 3]:
print 'id = %d' % i
for c in ['red', 'green', 'blue']:
print 'color = %s' % c
You can also specify a subarray.
colors = ['red', 'green', 'blue']
for c in colors[1:]:
print 'color = %s' % c
output
color = green
color = blue
There is a syntax for-else. The else clause is executed when the for loop processing is completed.
for i in range(0, 3):
print 'i = %d' % i
else:
print 'done'
output
i = 0
i = 1
i = 2
done
If you break in the middle, the else clause will not be executed.
for i in range(0, 3):
print 'i = %d' % i
if i == 1:
break
else:
print 'done' #Not executed
while statement. You can also use the else clause here.
i = 5
while 0 < i:
print 'id = %d' % i
i -= 1
else:
print 'done'
Enclose in '''.
val = '''this is a pen.
but it's not my favorite color.
I love red.
'''
If you want to indent and write in the code, there are the following description methods.
import textwrap
print textwrap.dedent('''\
AIUEO
Kakikukeko
SA Shi Su Se So''')
You can handle exceptions with the try-except-finally syntax, similar to Java's try-catch-finally syntax. Also, in Python, the else clause can be specified, and it is executed when the process is completed without the occurrence of an exception in try.
try:
val = int("123") # no exception
print 'val = %d' % val
except ValueError:
raise
else:
print '>> else'
finally:
print '>> finally'
In this case, Error / Exception does not occur in the try clause, so the output is as follows.
output
val = 123
>> else
>> finally
Dare to generate an Error in the try clause.
try:
val = int("abc") # ValueError
print 'val = %d' % val
except ValueError:
# raise
pass
else:
print '>> else'
finally:
print '>> finally'
In this case, the output will be:
output
>> finally
In addition, supplementary Errors and Exceptions can be specified collectively with ().
try:
...
except (XXXError, YYYError, ZZZException):
...
It can be defined as follows.
Member variables do not have to be declared one by one.
The first argument self is always required and does not need to be specified when calling.
class ClassName:
def __init__(self, arg1, arg2):
self.member1 = arg1
self.member2 = arg2
def method(self, param1):
// logic
Instantiation-> Call.
data = ClassName('nameA', 'nameB')
data.method('param1')
In the following example, print is not possible.
val = 120
print "val + " val
It can be explicitly converted to a string with str ().
printt "hoge=" + str(123)
Convert a string to an integer.
val = int("23")
If conversion is not possible, ValueError occurs.
try:
v = int("abc")
except ValueError:
print 'ValueError occurs'
Specify the second argument of int ()
value10 = int ('0xF6', 16)
For portability, don't use it.
import os
os.system('<command>')
(Example)
os.system('grep TvC -R .')
You can receive the result of the system command as a character string. When there is no result, it seems that an empty string is returned instead of None.
This is also portable and will not be used extensively.
import commands
r = commands.getoutput('<command>')
(Example)
r = commands.getoutput('date')
You can use if --elif.
Numeric types can also be objects (immutable) and cannot be written as ʻi ++or--i. Use ʻi + = 1 and so on.
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