Python basic grammar (miscellaneous) Memo (3)

2.7 base. (1) is here. (2) is here.

function

Declared using the def keyword.

>>> def test(arg):
...    print(arg)
...
>>> test('hoge')

hoge

Argument keyword specification

>>> test(arg="hogehoge")

hogehoge

Variadic

If you add an asterisk before the argument, you can accept any number of arguments that do not specify a keyword.

>>> def test(a, b, *args):
...     print(a, b, args)
...
>>> test(1, 2, 3, 4, 5)

(1, 2, (3, 4, 5))

#OK even in the sky
>>> test(1, 2)

(1, 2, ())

#Keywords cannot be specified
>>> test(1, 2, args = 3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: test() got an unexpected keyword argument 'args'

Undefined keyword arguments

If you define an argument with two asterisks, you can take an undefined argument with a keyword specified.

>>> def test(a, b, **args):
...    print(a, b, args)
...
>>> test(1, 2, c=3, d=4)

1, 2, {'c' : 3, 'd' : 4} #Substituted as a dictionary

#No keyword is NG
>>> test(1, 2, 3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: test() takes exactly 2 arguments (3 given)

Arguments like * val and ** args should be at the end of the argument list

Default argument

>>> def test(arg="hogehoge"):
...    print(arg)
...
>>> test()

hogehoge

File operations

File type

Use the built-in function ʻopen ()`. The arguments are almost the same as C's fopen ().

>>> f = open("foo.txt", "r")
>>> s = f.read()  #Read all file contents
>>> f.close

#In python3 series, file encoding/Has an argument that specifies the text encoding used for decoding
# f = open("foo.txt", "r", encoding='utf-8')

Python2 series open: http://docs.python.jp/2/library/functions.html?highlight=open#open

Python3 series open: http://docs.python.jp/3/library/functions.html?highlight=open#open

I'll omit it here, but there's a lot of information about Unicode support in Python3. For example this. http://postd.cc/why-python-3-exists/

mode

The meaning of the second argument.

Read

f.read(size)

Reads the specified size (or the end of the file if omitted) from the file and returns a string.

f.readline(size)

Reads the specified number of lines (1 line if omitted) and returns a character string.

f.readlines(size)

Reads multiple lines from the file up to the specified number of lines (up to the end of the file if there is none) and returns a list with strings as elements.

sample: Process text file line by line

>>> f = open("test.txt", 'r')
>>> for line in f:
...    print(line, end=" ")   #Display line by line

Export

f.write(str)

Write to a file by specifying a character string.

f.writelines(sequence)

Takes a sequence (list, etc.) that includes a string as an argument and writes it to a file (no newline character is added for each element).