Python實現遍歷讀取文件或文件夾
搞機器學習或者深度學習算法很多時候需要遍歷某個目錄讀取文件，特別是經常需要讀取某個特定後綴的文件，比如圖片的話可能需要讀取jpg, png, bmp格式的文件。python本身的庫函數功能沒有這麼定制化，所以就需要再重新包裝一下。
例子
假設我們有如下的目錄結構，以bmp結尾的是文件，其他是文件夾。下面的程序都將以該目錄結構為例進行說明。
os.listdir
os.listdir僅讀取當前路徑下的文件和文件夾，返回一個列表。讀取demo目錄結構的代碼和結果如下：
path = r'D:\data' items = os.listdir(path) # ==> ['1.bmp', '2.bmp', 'a', 'b']
os.walk
os.walk本身已經是遍歷讀取，包含所有的子文件（夾）但是其結果不像是os.listdir一樣是個list，而是一個比較復雜的數據體，難以直接使用，所以一般需要再處理一下。我們可以使用for語句將其打印出來看看：
path = r'D:\data'
# part 1
for items in os.walk(path):
print(items)
# part 2
for main_dir, sub_dir_list, sub_file_list in os.walk(path):
print(main_dir, sub_dir_list, sub_file_list)
結果為：
# part 1
('D:\\data', ['a', 'b'], ['1.bmp', '2.bmp'])
('D:\\data\\a', [], ['a1.bmp'])
('D:\\data\\b', [], ['b1.bmp'])# part 2
D:\data ['a', 'b'] ['1.bmp', '2.bmp']
D:\data\a [] ['a1.bmp']
D:\data\b [] ['b1.bmp']
使用迭代器對os.walk()的結果進行輸出，發現每一條包含三個部分（part 1），在part 2中，我們給三個部分分別起名為main_dir, sub_dir_list, sub_file_list，下面對其進行簡單解釋：
- main_dir：遍歷得到的路徑下所有文件夾
- sub_dir_list：main_dir下面的文件夾
- sub_file_list：main_dir下面的文件
連接main_dir和sub_file_list中的文件可以得到路徑下的所有文件。
sub_dir_list在這裡則沒有用處，我們無需再去遍歷sub_dir_list，因為它們已經包含在main_dir裡瞭。
遍歷讀取代碼
代碼邏輯如下：
需要有後綴辨別功能，並且能夠同時辨別多個後綴
需要有遞歸和非遞歸功能
返回的是以入參path為前綴的路徑，所以如果path是完整路徑那麼返回的就是完整路徑，否則就不是
# -*- coding: utf-8 -*-
import os
def file_ext(filename, level=1):
"""
return extension of filename
Parameters:
-----------
filename: str
name of file, path can be included
level: int
level of extension.
for example, if filename is 'sky.png.bak', the 1st level extension
is 'bak', and the 2nd level extension is 'png'
Returns:
--------
extension of filename
"""
return filename.split('.')[-level]
def _contain_file(path, extensions):
"""
check whether path contains any file whose extension is in extensions list
Parameters:
-----------
path: str
path to be checked
extensions: str or list/tuple of str
extension or extensions list
Returns:
--------
return True if contains, else return False
"""
assert os.path.exists(path), 'path must exist'
assert os.path.isdir(path), 'path must be dir'
if isinstance(extensions, str):
extensions = [extensions]
for file in os.listdir(path):
if os.path.isfile(os.path.join(path, file)):
if (extensions is None) or (file_ext(file) in extensions):
return True
return False
def _process_extensions(extensions=None):
"""
preprocess and check extensions, if extensions is str, convert it to list.
Parameters:
-----------
extensions: str or list/tuple of str
file extensions
Returns:
--------
extensions: list/tuple of str
file extensions
"""
if extensions is not None:
if isinstance(extensions, str):
extensions = [extensions]
assert isinstance(extensions, (list, tuple)), \
'extensions must be str or list/tuple of str'
for ext in extensions:
assert isinstance(ext, str), 'extension must be str'
return extensions
def get_files(path, extensions=None, is_recursive=True):
"""
read files in path. if extensions is None, read all files, if extensions
are specified, only read the files who have one of the extensions. if
is_recursive is True, recursively read all files, if is_recursive is False,
only read files in current path.
Parameters:
-----------
path: str
path to be read
extensions: str or list/tuple of str
file extensions
is_recursive: bool
whether read files recursively. read recursively is True, while just
read files in current path if False
Returns:
--------
files: the obtained files in path
"""
extensions = _process_extensions(extensions)
files = []
# get files in current path
if not is_recursive:
for name in os.listdir(path):
fullname = os.path.join(path, name)
if os.path.isfile(fullname):
if (extensions is None) or (file_ext(fullname) in extensions):
files.append(fullname)
return files
# get files recursively
for main_dir, _, sub_file_list in os.walk(path):
for filename in sub_file_list:
fullname = os.path.join(main_dir, filename)
if (extensions is None) or (file_ext(fullname) in extensions):
files.append(fullname)
return files
def get_folders(path, extensions=None, is_recursive=True):
"""
read folders in path. if extensions is None, read all folders, if
extensions are specified, only read the folders who contain any files that
have one of the extensions. if is_recursive is True, recursively read all
folders, if is_recursive is False, only read folders in current path.
Parameters:
-----------
path: str
path to be read
extensions: str or list/tuple of str
file extensions
is_recursive: bool
whether read folders recursively. read recursively is True, while just
read folders in current path if False
Returns:
--------
folders: the obtained folders in path
"""
extensions = _process_extensions(extensions)
folders = []
# get folders in current path
if not is_recursive:
for name in os.listdir(path):
fullname = os.path.join(path, name)
if os.path.isdir(fullname):
if (extensions is None) or \
(_contain_file(fullname, extensions)):
folders.append(fullname)
return folders
# get folders recursively
for main_dir, _, _ in os.walk(path):
if (extensions is None) or (_contain_file(main_dir, extensions)):
folders.append(main_dir)
return folders
if __name__ == '__main__':
path = r'.\data'
files = get_files(path)
print(files) # ==> ['D:\\data\\1.bmp', 'D:\\data\\2.bmp', 'D:\\data\\a\\a1.bmp', 'D:\\data\\b\\b1.bmp']
folders = get_folders(path)
print(folders) # ==> ['D:\\data', 'D:\\data\\a', 'D:\\data\\b']
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