The generated form used to create the list.
To generate list [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], you can use list(range(1, 11)): note 11
>>> list(range(1, 11)) [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
How to generate [1x1, 2x2, 3X3,..., 10x10]? The first method is circulation:
>>> L = [] >>> for x in range(1, 11): ... L.append(x * x) ... >>> L [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
However, the cycle is too cumbersome, and the list generation can use one line of statements instead of the cycle to generate the above list:
>>> [x * x for x in range(1, 11)] [1, 4, 9, 16, 25, 36, 49, 64, 81, 100]
When writing list generation, put the element x * x to be generated first, followed by the for loop
You can also use two layers of loops to generate a full spread:
>>> [m + n for m in 'ABC' for n in 'XYZ'] ['AX', 'AY', 'AZ', 'BX', 'BY', 'BZ', 'CX', 'CY', 'CZ']
List all the files and directory names in the current directory, which can be realized by one line of code:
>>> import os # Import the os module. The concept of the module will be discussed later >>> [d for d in os.listdir('.')] # os.listdir can list files and directories ['.emacs.d', '.ssh', '.Trash', 'Adlm', 'Applications', 'Desktop', 'Documents', 'Downloads', 'Library', 'Movies', 'Music', 'Pictures', 'Public', 'VirtualBox VMs', 'Workspace', 'XCode']
items() of dict can iterate key and value at the same time:
>>> d = {'x': 'A', 'y': 'B', 'z': 'C' } >>> for k, v in d.items(): ... print(k, '=', v) ... y = B x = A z = C
Therefore, list generation can also use two variables to generate a list:
>>> d = {'x': 'A', 'y': 'B', 'z': 'C' } >>> [k + '=' + v for k, v in d.items()] ['y=B', 'x=A', 'z=C']
Finally, change all strings in a list to lowercase:
>>> L = ['Hello', 'World', 'IBM', 'Apple'] >>> [s.lower() for s in L] ['hello', 'world', 'ibm', 'apple']
Practice
If the list contains both strings and integers, since there is no lower() method for non string types, the list generation will report an error:
>>> L = ['Hello', 'World', 18, 'Apple', None] >>> [s.lower() for s in L] Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<stdin>", line 1, in <listcomp> AttributeError: 'int' object has no attribute 'lower'
Use the built-in isinstance function to determine whether a variable is a string:
>>> x = 'abc' >>> y = 123 >>> isinstance(x, str) True >>> isinstance(y, str) False
Please modify the list generation. Add if statement to ensure that the list generation can execute correctly:
L1 = ['Hello', 'World', 18, 'Apple', None] s=[L2.lower() for L2 in L1 if isinstance(L2,str)==1] print(s)