tqdm_note
2022/09/19
4-minute read
tqdm
在看别人写的代码的时候发现的tqdm模块，当时还很好奇，这命名不像是标准库函数，于是乎去搜索了一下，是一个显示进度条的库
演示
试看如下代码：
from tqdm import tqdm
from time import sleep
for i in tqdm(range(0, 100), desc="加载中", colour="green"):
sleep(1)
加载中: 70%|███████ | 70/100 [01:10<00:30, 1.01s/it]
当时第一次看得时候不太理解 01:10<00:30 这种显示方式，对此感到非常的不舒服，想要调整一下格式，去网上搜了搜tqdm的教程，发现清一色都是tqdm(range()),事实上和官方提供的大同小异，官方文档提供的例子更为丰富一些。
多次查找无果后，深感自己阅读文档的水平不足。
提高
为了解决 01:10<00:30 这个问题，忽而记起网上对tqdm库的描述，这是个纯python实现的库。点进去看源码，文件名std.py。
def __init__(self, iterable=None, desc=None, total=None, leave=True, file=None,
ncols=None, mininterval=0.1, maxinterval=10.0, miniters=None,
ascii=None, disable=False, unit='it', unit_scale=False,
dynamic_ncols=False, smoothing=0.3, bar_format=None, initial=0,
position=None, postfix=None, unit_divisor=1000, write_bytes=None,
lock_args=None, nrows=None, colour=None, delay=0, gui=False,
**kwargs):
"""
Parameters
----------
iterable : iterable, optional
Iterable to decorate with a progressbar.
Leave blank to manually manage the updates.
desc : str, optional
Prefix for the progressbar.
total : int or float, optional
The number of expected iterations. If unspecified,
len(iterable) is used if possible. If float("inf") or as a last
resort, only basic progress statistics are displayed
(no ETA, no progressbar).
If `gui` is True and this parameter needs subsequent updating,
specify an initial arbitrary large positive number,
e.g. 9e9.
leave : bool, optional
If [default: True], keeps all traces of the progressbar
upon termination of iteration.
If `None`, will leave only if `position` is `0`.
file : `io.TextIOWrapper` or `io.StringIO`, optional
Specifies where to output the progress messages
(default: sys.stderr). Uses `file.write(str)` and `file.flush()`
methods. For encoding, see `write_bytes`.
ncols : int, optional
The width of the entire output message. If specified,
dynamically resizes the progressbar to stay within this bound.
If unspecified, attempts to use environment width. The
fallback is a meter width of 10 and no limit for the counter and
statistics. If 0, will not print any meter (only stats).
mininterval : float, optional
Minimum progress display update interval [default: 0.1] seconds.
maxinterval : float, optional
Maximum progress display update interval [default: 10] seconds.
Automatically adjusts `miniters` to correspond to `mininterval`
after long display update lag. Only works if `dynamic_miniters`
or monitor thread is enabled.
miniters : int or float, optional
Minimum progress display update interval, in iterations.
If 0 and `dynamic_miniters`, will automatically adjust to equal
`mininterval` (more CPU efficient, good for tight loops).
If > 0, will skip display of specified number of iterations.
Tweak this and `mininterval` to get very efficient loops.
If your progress is erratic with both fast and slow iterations
(network, skipping items, etc) you should set miniters=1.
ascii : bool or str, optional
If unspecified or False, use unicode (smooth blocks) to fill
the meter. The fallback is to use ASCII characters " 123456789#".
disable : bool, optional
Whether to disable the entire progressbar wrapper
[default: False]. If set to None, disable on non-TTY.
unit : str, optional
String that will be used to define the unit of each iteration
[default: it].
unit_scale : bool or int or float, optional
If 1 or True, the number of iterations will be reduced/scaled
automatically and a metric prefix following the
International System of Units standard will be added
(kilo, mega, etc.) [default: False]. If any other non-zero
number, will scale `total` and `n`.
dynamic_ncols : bool, optional
If set, constantly alters `ncols` and `nrows` to the
environment (allowing for window resizes) [default: False].
smoothing : float, optional
Exponential moving average smoothing factor for speed estimates
(ignored in GUI mode). Ranges from 0 (average speed) to 1
(current/instantaneous speed) [default: 0.3].
bar_format : str, optional
Specify a custom bar string formatting. May impact performance.
[default: '{l_bar}{bar}{r_bar}'], where
l_bar='{desc}: {percentage:3.0f}%|' and
r_bar='| {n_fmt}/{total_fmt} [{elapsed}<{remaining}, '
'{rate_fmt}{postfix}]'
Possible vars: l_bar, bar, r_bar, n, n_fmt, total, total_fmt,
percentage, elapsed, elapsed_s, ncols, nrows, desc, unit,
rate, rate_fmt, rate_noinv, rate_noinv_fmt,
rate_inv, rate_inv_fmt, postfix, unit_divisor,
remaining, remaining_s, eta.
Note that a trailing ": " is automatically removed after {desc}
if the latter is empty.
initial : int or float, optional
The initial counter value. Useful when restarting a progress
bar [default: 0]. If using float, consider specifying `{n:.3f}`
or similar in `bar_format`, or specifying `unit_scale`.
position : int, optional
Specify the line offset to print this bar (starting from 0)
Automatic if unspecified.
Useful to manage multiple bars at once (eg, from threads).
postfix : dict or *, optional
Specify additional stats to display at the end of the bar.
Calls `set_postfix(**postfix)` if possible (dict).
unit_divisor : float, optional
[default: 1000], ignored unless `unit_scale` is True.
write_bytes : bool, optional
If (default: None) and `file` is unspecified,
bytes will be written in Python 2. If `True` will also write
bytes. In all other cases will default to unicode.
lock_args : tuple, optional
Passed to `refresh` for intermediate output
(initialisation, iterating, and updating).
nrows : int, optional
The screen height. If specified, hides nested bars outside this
bound. If unspecified, attempts to use environment height.
The fallback is 20.
colour : str, optional
Bar colour (e.g. 'green', '#00ff00').
delay : float, optional
Don't display until [default: 0] seconds have elapsed.
gui : bool, optional
WARNING: internal parameter - do not use.
Use tqdm.gui.tqdm(...) instead. If set, will attempt to use
matplotlib animations for a graphical output [default: False].
以往看一些源码都是一堆说明然后写个pass，这种实现方式一般都是使用c语言实现的，源码看起来会比较麻烦。而纯python实现的那可太好了。
bar_format 这个参数，想来就是我想要的了，看一下注释里bar_format的描述 default: ‘{l_bar}{bar}{r_bar}',试了试就理解了这三个参数的意义，很可惜的是依然不能解决我的问题。
再深入往里看，r_bar这个参数引起了我的注意，这应该就是我关注的部分了。随后找到format_meter函数，找到如下代码：
r_bar = '| {0}/{1} [{2}<{3}, {4}{5}]'.format(n_fmt, total_fmt, elapsed_str, remaining_str, rate_fmt, postfix)
至此算是完了，但又没完。我翻遍整个std.py文件，没找到单独设置r_bar的地方，有的只是bar_format，换句话说就是原作者并没有对这个进行支持，所以无可奈何。除了直接修改tqdm源码，暂时没有想到更简单的办法，有些遗憾。
结语
对于纯python的第三方库，感到极其亲切，不像是底层c语言实现的一些标准库，看到一个空函数，一堆文字描述加上pass，实在是感到沮丧。直接阅读代码比阅读文档的方式可能来得更直接易于理解，仅仅是对于我而已，仅仅限制在对于tqdm库而言。
通常都是直接找官方文档，阅读源码的方式也不失为一种很好的办法，这种交流更为直接，明晰。