matplotlib之pyplot模块——调整子图布局（subplots_adjust、tight

在pyplot模块中，与调整子图布局的函数主要为subplots_adjust和tight_layout，其中subplots_adjust是修改子图间距的通用函数，tight_layout默认执行一种固定的间距配置，也可以自定义间距配置，底层原理类似于subplots_adjust函数。

`subplots_adjust`函数概述

subplots_adjust函数的功能为调整子图的布局参数。对于没有设置的参数保持不变，初始值由rcParams["figure.subplot.[name]"]提供。

函数的签名为matplotlib.pyplot.subplots_adjust(left=None, bottom=None, right=None, top=None, wspace=None, hspace=None)

函数的参数如下：

left：所有子图整体相对于图像的左外边距，距离单位为图像宽度的比例（小数）。可选参数。浮点数。默认值为0.125。
right：所有子图整体相对于图像的右外边距，距离单位为图像宽度的比例（小数）。可选参数。浮点数。默认值为0.0。
bottom：所有子图整体相对于图像的下外边距，距离单位为图像高度的比例（小数）。可选参数。浮点数。默认值为0.11。
top：所有子图整体相对于图像的上外边距，距离单位为图像高度的比例（小数）。可选参数。浮点数。默认值为0.88。
wspace：子图间宽度内边距，距离单位为子图平均宽度的比例（小数）。浮点数。默认值为0.2。
hspace：子图间高度内边距，距离单位为子图平均高度的比例（小数）。可选参数。浮点数。默认值为0.2。

rcParams["figure.subplot.[name]"]的值如下：

## The figure subplot parameters.  All dimensions are a fraction of the figure width and height.
#figure.subplot.left:   0.125  # the left side of the subplots of the figure
#figure.subplot.right:  0.9    # the right side of the subplots of the figure
#figure.subplot.bottom: 0.11   # the bottom of the subplots of the figure
#figure.subplot.top:    0.88   # the top of the subplots of the figure
#figure.subplot.wspace: 0.2    # the amount of width reserved for space between subplots,# expressed as a fraction of the average axis width
#figure.subplot.hspace: 0.2    # the amount of height reserved for space between subplots,# expressed as a fraction of the average axis height

`subplots_adjust`函数原理

根据以下源码可知，子图间距的默认设置即rcParams["figure.subplot.[name]"]，使用subplots_adjust函数调整后，间距配置保存在figure.subplotpars。

pyplot.subplots_adjust()源码

def subplots_adjust(left=None, bottom=None, right=None, top=None, wspace=None,hspace=None):return gcf().subplots_adjust(left=left, bottom=bottom, right=right, top=top, wspace=wspace,hspace=hspace)

figure.Figure.subplots_adjust()源码

def subplots_adjust(self, left=None, bottom=None, right=None, top=None,wspace=None, hspace=None):if self.get_constrained_layout():self.set_constrained_layout(False)_api.warn_external("This figure was using constrained_layout, but that is ""incompatible with subplots_adjust and/or tight_layout; ""disabling constrained_layout.")self.subplotpars.update(left, bottom, right, top, wspace, hspace)for ax in self.axes:if isinstance(ax, SubplotBase):ax._set_position(ax.get_subplotspec().get_position(self))self.stale = True

figure.Figure.__init__()源码

if subplotpars is None:subplotpars = SubplotParams()self.subplotpars = subplotpars

figure.SubplotParams类源码

class SubplotParams:"""A class to hold the parameters for a subplot."""def __init__(self, left=None, bottom=None, right=None, top=None,wspace=None, hspace=None):self.validate = Truefor key in ["left", "bottom", "right", "top", "wspace", "hspace"]:setattr(self, key, mpl.rcParams[f"figure.subplot.{key}"])self.update(left, bottom, right, top, wspace, hspace)def update(self, left=None, bottom=None, right=None, top=None,wspace=None, hspace=None):"""Update the dimensions of the passed parameters. *None* means unchanged."""if self.validate:if ((left if left is not None else self.left)>= (right if right is not None else self.right)):raise ValueError('left cannot be >= right')if ((bottom if bottom is not None else self.bottom)>= (top if top is not None else self.top)):raise ValueError('bottom cannot be >= top')if left is not None:self.left = leftif right is not None:self.right = rightif bottom is not None:self.bottom = bottomif top is not None:self.top = topif wspace is not None:self.wspace = wspaceif hspace is not None:self.hspace = hspace

案例：`subplots_adjust()`修改间距验证

import matplotlib.pyplot as plt# 原始间距配置
fig,ax=plt.subplots(3,3)
print(vars(fig.subplotpars))
# 通过subplots_adjust()设置间距配置
plt.subplots_adjust(left=0.1,bottom=0.1,right=0.9,top=0.9,wspace=0.1,hspace=0.1)
print(vars(fig.subplotpars))
plt.show()

输出：

{'validate': True, 'left': 0.125, 'bottom': 0.125, 'right': 0.9, 'top': 0.88, 'wspace': 0.2, 'hspace': 0.2}
{'validate': True, 'left': 0.1, 'bottom': 0.1, 'right': 0.9, 'top': 0.9, 'wspace': 0.1, 'hspace': 0.1}

原始间距设置

subplots_adjust()修改间距后

`tight_layout`函数概述

tight_layout函数的功能为子图的内边距。备注：对axes()函数生成的子图无效。

函数的签名为matplotlib.pyplot.tight_layout(*, pad=1.08, h_pad=None, w_pad=None, rect=None)

函数的参数如下：

pad：所有子图整体边缘相对于图像边缘的内边距，距离单位为字体大小的比例（小数，与rcParams["font.size"]相关）。可选参数。浮点数。默认值为1.08。
h_pad, w_pad：子图之间的内边距，距离单位为字体大小的比例（小数）。可选参数。浮点数。默认值为pad。
rect：绘制子图的矩形区域的归一化坐标。可选参数。4元组(left, bottom, right, top)。默认值为(0, 0, 1, 1)。

`tight_layout`函数原理

根据以下源码可知pyplot.tight_layout()函数主要通过matplotlib.tight_layout模块相关函数构造子图间距设置，最终通过figure.Figure.subplots_adjust函数更新设置。

pyplot.tight_layout()源码

def tight_layout(pad=1.08, h_pad=None, w_pad=None, rect=None):gcf().tight_layout(pad=pad, h_pad=h_pad, w_pad=w_pad, rect=rect)

figure.Figure.tight_layout()源码

def tight_layout(self, *, pad=1.08, h_pad=None, w_pad=None, rect=None):from .tight_layout import (get_renderer, get_subplotspec_list, get_tight_layout_figure)from contextlib import suppresssubplotspec_list = get_subplotspec_list(self.axes)if None in subplotspec_list:_api.warn_external("This figure includes Axes that are not ""compatible with tight_layout, so results ""might be incorrect.")renderer = get_renderer(self)ctx = (renderer._draw_disabled()if hasattr(renderer, '_draw_disabled')else suppress())with ctx:kwargs = get_tight_layout_figure(self, self.axes, subplotspec_list, renderer,pad=pad, h_pad=h_pad, w_pad=w_pad, rect=rect)if kwargs:self.subplots_adjust(**kwargs)

案例：应用`tight_layout`后验证间距配置

import matplotlib.pyplot as plt# 原始间距配置
fig,ax=plt.subplots(3,3)
print(vars(fig.subplotpars))
# 设置tight_layout之后的默认间距配置
plt.tight_layout()
print(vars(fig.subplotpars))
# 设置tight_layout内边距之后的间距配置
plt.tight_layout(h_pad=2.5,w_pad=2.5)
print(vars(fig.subplotpars))
plt.show()

输出为：

{'validate': True, 'left': 0.125, 'bottom': 0.125, 'right': 0.9, 'top': 0.88, 'wspace': 0.2, 'hspace': 0.2}
{'validate': True, 'left': 0.0779513888888889, 'bottom': 0.09652777777777778, 'right': 0.9566261574074074, 'top': 0.9486111111111112, 'wspace': 0.42123244337593335, 'hspace': 0.5247524752475248}
{'validate': True, 'left': 0.0779513888888889, 'bottom': 0.0965277777777778, 'right': 0.9566261574074075, 'top': 0.9486111111111111, 'wspace': 0.6248542240052247, 'hspace': 0.8996088657105613}

扩展

通过设置rcParams['figure.autolayout']=True可图像自动应用tight_layout。

## Figure layout
#figure.autolayout: False  # When True, automatically adjust subplot# parameters to make the plot fit the figure# using `tight_layout`
#figure.constrained_layout.use: False  # When True, automatically make plot# elements fit on the figure. (Not# compatible with `autolayout`, above).
#figure.constrained_layout.h_pad:  0.04167  # Padding around axes objects. Float representing
#figure.constrained_layout.w_pad:  0.04167  # inches. Default is 3/72 inches (3 points)
#figure.constrained_layout.hspace: 0.02     # Space between subplot groups. Float representing
#figure.constrained_layout.wspace: 0.02     # a fraction of the subplot widths being separated.