文字和文字位置
通过plt.text()或ax.text()命令可在图形上添加文字。
Signature:
ax.text(x, y, s, fontdict=None, withdash=<deprecated parameter>, **kwargs)
Docstring:
Add text to the axes.
Add the text *s* to the axes at location *x*, *y* in data coordinates.
Parameters
----------
x, y : scalars
The position to place the text. By default, this is in data
coordinates. The coordinate system can be changed using the
*transform* parameter.
s : str
The text.
fontdict : dictionary, optional, default: None
A dictionary to override the default text properties. If fontdict
is None, the defaults are determined by your rc parameters.
withdash : boolean, optional, default: False
Creates a `~matplotlib.text.TextWithDash` instance instead of a
`~matplotlib.text.Text` instance.
Returns
-------
text : `.Text`
The created `.Text` instance.
Other Parameters
----------------
**kwargs : `~matplotlib.text.Text` properties.
Other miscellaneous text parameters.
Examples
--------
Individual keyword arguments can be used to override any given
parameter::
>>> text(x, y, s, fontsize=12)
The default transform specifies that text is in data coords,
alternatively, you can specify text in axis coords (0,0 is
lower-left and 1,1 is upper-right). The example below places
text in the center of the axes::
>>> text(0.5, 0.5, 'matplotlib', horizontalalignment='center',
... verticalalignment='center', transform=ax.transAxes)
You can put a rectangular box around the text instance (e.g., to
set a background color) by using the keyword `bbox`. `bbox` is
a dictionary of `~matplotlib.patches.Rectangle`
properties. For example::
>>> text(x, y, s, bbox=dict(facecolor='red', alpha=0.5))
text函数中transform参数用于设置坐标变换，Matplotlib一共有三种方式设置文字位置：
- ax.transData : 默认的，以数据为基准的坐标变换（x轴和y轴的标签作为数据坐标）；
- ax.transAxes: 以坐标轴为基准的坐标变换（以坐标轴左下角原点，按坐标轴尺寸的比例呈现坐标）；
- fig.transFigure:以图形为基准的坐标变换（以图纸左下角原点，按图形尺寸的比例呈现坐标）。
三个坐标系呈现的文字都是左对齐，当改变坐标轴上下限时，只有transData坐标会受影响，其它两个坐标系不变。
fig, ax = plt.subplots(facecolor='lightgray')
ax.axis([0, 10, 0, 10])
ax.text(1, 5, ".Data:(1, 5)", transform=ax.transData)
ax.text(0.5, 0.1, ".Axes:(0.5, 0.1)", transform=ax.transAxes)
ax.text(0.2, 0.2, ".Figure:(0.2, 0.2)", transform=fig.transFigure)
ax.set_xlim(0, 2)
ax.set_ylim(-6, 6)
fig
箭头和注释
Matplotlib中plt.annotate()/ax.annotate()函数可用于创建文字以及箭头等。
Signature:
ax.annotate(s, xy, *args, **kwargs)
Docstring:
Annotate the point *xy* with text *text*.
In the simplest form, the text is placed at *xy*.
Optionally, the text can be displayed in another position *xytext*.
An arrow pointing from the text to the annotated point *xy* can then
be added by defining *arrowprops*.
Parameters
----------
text : str
The text of the annotation. *s* is a deprecated synonym for this
parameter.
xy : (float, float)
The point *(x,y)* to annotate.
xytext : (float, float), optional
The position *(x,y)* to place the text at.
If *None*, defaults to *xy*.
xycoords : str, `.Artist`, `.Transform`, callable or tuple, optional
The coordinate system that *xy* is given in. The following types
of values are supported:
- One of the following strings:
================= =============================================
Value Description
================= =============================================
'figure points' Points from the lower left of the figure
'figure pixels' Pixels from the lower left of the figure
'figure fraction' Fraction of figure from lower left
'axes points' Points from lower left corner of axes
'axes pixels' Pixels from lower left corner of axes
'axes fraction' Fraction of axes from lower left
'data' Use the coordinate system of the object being
annotated (default)
'polar' *(theta,r)* if not native 'data' coordinates
================= =============================================
- An `.Artist`: *xy* is interpreted as a fraction of the artists
`~matplotlib.transforms.Bbox`. E.g. *(0, 0)* would be the lower
left corner of the bounding box and *(0.5, 1)* would be the
center top of the bounding box.
- A `.Transform` to transform *xy* to screen coordinates.
- A function with one of the following signatures::
def transform(renderer) -> Bbox
def transform(renderer) -> Transform
where *renderer* is a `.RendererBase` subclass.
The result of the function is interpreted like the `.Artist` and
`.Transform` cases above.
- A tuple *(xcoords, ycoords)* specifying separate coordinate
systems for *x* and *y*. *xcoords* and *ycoords* must each be
of one of the above described types.
See :ref:`plotting-guide-annotation` for more details.
Defaults to 'data'.
textcoords : str, `.Artist`, `.Transform`, callable or tuple, optional
The coordinate system that *xytext* is given in.
All *xycoords* values are valid as well as the following
strings:
================= =========================================
Value Description
================= =========================================
'offset points' Offset (in points) from the *xy* value
'offset pixels' Offset (in pixels) from the *xy* value
================= =========================================
Defaults to the value of *xycoords*, i.e. use the same coordinate
system for annotation point and text position.
arrowprops : dict, optional
The properties used to draw a
`~matplotlib.patches.FancyArrowPatch` arrow between the
positions *xy* and *xytext*.
If *arrowprops* does not contain the key 'arrowstyle' the
allowed keys are:
========== ======================================================
Key Description
========== ======================================================
width The width of the arrow in points
headwidth The width of the base of the arrow head in points
headlength The length of the arrow head in points
shrink Fraction of total length to shrink from both ends
? Any key to :class:`matplotlib.patches.FancyArrowPatch`
========== ======================================================
If *arrowprops* contains the key 'arrowstyle' the
above keys are forbidden. The allowed values of
``'arrowstyle'`` are:
============ =============================================
Name Attrs
============ =============================================
``'-'`` None
``'->'`` head_length=0.4,head_width=0.2
``'-['`` widthB=1.0,lengthB=0.2,angleB=None
``'|-|'`` widthA=1.0,widthB=1.0
``'-|>'`` head_length=0.4,head_width=0.2
``'<-'`` head_length=0.4,head_width=0.2
``'<->'`` head_length=0.4,head_width=0.2
``'<|-'`` head_length=0.4,head_width=0.2
``'<|-|>'`` head_length=0.4,head_width=0.2
``'fancy'`` head_length=0.4,head_width=0.4,tail_width=0.4
``'simple'`` head_length=0.5,head_width=0.5,tail_width=0.2
``'wedge'`` tail_width=0.3,shrink_factor=0.5
============ =============================================
Valid keys for `~matplotlib.patches.FancyArrowPatch` are:
=============== ==================================================
Key Description
=============== ==================================================
arrowstyle the arrow style
connectionstyle the connection style
relpos default is (0.5, 0.5)
patchA default is bounding box of the text
patchB default is None
shrinkA default is 2 points
shrinkB default is 2 points
mutation_scale default is text size (in points)
mutation_aspect default is 1.
? any key for :class:`matplotlib.patches.PathPatch`
=============== ==================================================
Defaults to None, i.e. no arrow is drawn.
annotation_clip : bool or None, optional
Whether to draw the annotation when the annotation point *xy* is
outside the axes area.
- If *True*, the annotation will only be drawn when *xy* is
within the axes.
- If *False*, the annotation will always be drawn.
- If *None*, the annotation will only be drawn when *xy* is
within the axes and *xycoords* is 'data'.
Defaults to *None*.
**kwargs
Additional kwargs are passed to `~matplotlib.text.Text`.
fig, ax = plt.subplots()
x = np.linspace(0, 20, 1000)
ax.plot(x, np.cos(x))
ax.axis('equal')
#arrowprops用于设置箭头风格，xy设置箭头位置，xytext设置文字位置
ax.annotate('local maximum', xy=(6.28, 1), xytext=(10, 4),
arrowprops=dict(facecolor='black', shrink=0.05))
ax.annotate('local minimum', xy=(5 * np.pi, -1), xytext=(2, -6),
arrowprops=dict(arrowstyle="->",connectionstyle="angle3,angleA=0,angleB=90"))